This is intresting!

I live and drive at about 8000 ft, and have 3 V10 excursions.

The one with 120,000 miles on it runs hard and strong with 3.73 gears.

The one with 240,000 miles on it is a pooch with 3.73 gears.

The last one with 4.30 gears is supercharged and has 113,000 miles. It runs .......let's say strong enough.

I can pull 12,000 lbs with my 120,000 mile X with no issues like you are having.

How many miles are on your X?
Are brakes in good repair?
Is front end confirmed unlocked?
Was brake controller functioning correctly?

you said plugs were new....what about coils and are injectors spraying good?

My personal opinion is a good freshen up will do wonders. Refurbished injectors, new coils, new O2 sensors, new MAF, IAC, and make sure fuel pump and fpr are functioning correctly. Make sure alternator and battery are within spec. A low voltage situation will affect power.
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What I have noticed is that if a V10 uses over 1 qt of oil per 1000 to 1500 miles it's a pooch at my elevation. Bad rings and poor compression can run "OK" at low elevations. But up here 3000 ft above the mile high city of Denver.....where oxygen is 20% less than the low lands, low compression is standard. Add poor rings and now you have a pup of a pooch.
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Diesels are not exempt from power losses at 8000 ft. They have turbos to compensate for power losses. A gas motor with a turbo would compensate too.

 

Ha, yeah I guess that's an option. I use my 4wd quite often though. Just yesterday we went out to the desert to do some shooting and had to use 4wd in the sand to get back to the road. I can't even back out of my shop if there's snow on the ground because the driveway coming out is pretty steep.
Something to think about though.

 

Well, I am on 32.6" tires so that's bound to make a difference, lowering final drive ratio.
Truck has 200k on it, just rolled over to that on this trip. It runs like a beast with no trailer, smooth quiet and strong. I don't have any reason to suspect injectors aren't spraying well at this point.
Brakes are all good, I went through and replaced some sticking slide pins and all new pads before the trip, also a rear caliper was hanging up. Brake controller is working well, not dragging.
Front hubs are unlocked because I have to lock them manually at this point to use 4x4.
Voltage is 13.x when running.

You thinkk coils could cause low power? I figure they're kind of a go/no go. If they're bad they're going to cause misfires but there's no record of any in the ECU.

 

It's entirely possible for 1 hub to be physically unlocked but still be engaged. .....double check that front end is not locked in.

How much oil does it use?

After 200k miles I would spend the $15 or so per injector to have them ultrasonically cleaned and refurbished.

High elevation affects fuel trims....less fuel needed due to low O2. Long term fuel trim was probably causing some minor issue. Once you get above 4500 ft a battery disconnect for a hour may be benificial. Resetting fuel trims.

Remember 310 hp at 8000 ft is about 250 hp. Add driveline loss and your close to 215 hp, add high miles and your under 200 hp to rear wheels at peak hp which is 4900 rpm. Same goes for torque at 3200 rpm peak.

your new equivilant gear ratio is 3.61:1

Adding a turbo to your V10 will be cheaper initally and in long run, than buying a diesel.

$4 to 5k will get you a good turbo setup.
Borg Warner 13009097056 with a .83 AR turbine housing.

 

265,000 miles on a 2003 V10. 4.88 gears on stock size tires. Pulls my 10k camper easily and I rarely ever have to turn it faster than 3500 rpm to maintain speed on the interstate. I get about 7 - 7.5 mpg towing the camper and around 11 mpg not towing. Gears will make all the difference.

 

Uses almost no oil. Checked it after 1100 miles and was barely below the top mark. I might pull a couple injectors after we get home and see how they look.
You're right about the elevation which I have considered. I'm coming from a 500 hp Duramax so the adjustment is quite difficult! OF course the lack of pulling power was apparent at home too as soon as I hit the freeway and some small hills in Indiana, so even without the elevation, it's a slug.
I"ve been looking around for SC kits for it but haven't seen much. Of course once I go FI, suddenly the trans becomes something that'll need attention and I don't know if I want to go down that road again. Trying to keep it simple which is why I'm considering gearing.
I wish I had my scan tool or I'd clear the fuel trims right now; I hadn't thought of that. Doesn't clearing ECU with a code reader reset them too? I can do that on my SCT tuner.

Cool...How fast are you running on the freeway? How much speed do you lose going up mountains? Are you pulling in OD?
I don't care too much about mileage since I only drive it on trips pulling a trailer.

 

Last trip I was staying between 70-75 most of the time. I can't really give an accurate measure of how much speed I lose on mountains. Coming up I-59 out of Birmingham to Chattanooga, I stayed in OD on all but a couple of the hills and that was because I got trapped in traffic. I don't remember dropping below 65 unless I had to slow down for traffic. I'm coming from a 7.3 powered F-350 and the V10 was a whole new experience. Once you learn to make it spin, you'll like it a lot more. Forget there is such a thing as exhaust temp and push that go pedal hard. Mine is pretty unhappy below 2500 in a pull and does great at 3500. I wouldn't be afraid to turn it 5000. I'm not concerned about dropping out of OD as long as I don't pull down enough to unlock the converter. We're headed up to Fort Mtn in a couple of weeks...steep and very twisty road so I'll see how it does there. I will say that I was very unimpressed with mine when I had the 3.73 gears.

 

Gears only raise rpm to utilize torque at lower speeds.

At elevation as OP stated that power is not there, reguardless of what gears he has.

I guess OP could have put X in 4x4 low and had plenty of rpm at any speed under 40 mph.....maybe. But no "more" power.

At some point more power is needed. That's why the turbo diesel was mentioned. Turbos compensate for elevation and lower gears are not needed.

$2K for a gear swap and you have no more power?
Than at some point the front diff needs addressed. ...another $2K?

Gears have their place but not as a replacement for power.....expecially at high elevations.

one thing I will mention.
if the IAT sensor in maf was reading air temp above 120 either because of a malfunction or it was just hot, the PCM will retard timing which will cause significant power loss.

 

 

Good info that's what I'm looking for. Tom above said the same thing. I should be fine until the elevation makes the air thin, at that point not much can be done. So towing around home in the SE the gears will do just fine. Once I get to Colorado and some of Utah, the thin air will cause serious power loss. I think I'll accept that as long as the rest of the trip is painless. It really is a tough transition from a diesel that's for sure.

right, the elevation is going to suck a lot of power out no matter what RPM I"m at. However, I live in the SE so it will only affect me when I'm out West. That being said, I'm coming from diesel trucks for the last 10 years so I got spoiled when towing. I just don''t know what to do. I really don't want a 15+ year old diesel Excursion no matter how "well maintained" it is. Age does take it's toll on vehicles. And I'm kind of out of the phase of big engine swaps, otherwise I'd do a 12V Cummins. I just don't want the thing sitting there taking up all my time and money for months before it's done. It's not a project truck, i'ts a tow rig and it just needs to run and go reliably.

I was actually monitoring IAT and saw about 110 at the most.

I"m on 32.6" tires. (305/65/17)

 

 

That's what I thought too from his pictures, they look more like 34"s, but anything over stock is only going to make the performance of a 3.73 6.8 EX even more lacking.

 

True, I forgot how much even a small tire size change will affect a gasser.

 

Kai Herrmann...you said you lived in the SE. I'm in northwest Ga between Dalton Ga and Cleveland Tn. If you're close enough, you're welcome to take my Ex for a ride and see what you think about the V10/4.88 combo before you spend any money. Bring your trailer if you want...my V10 ain't skeered.

 

9 MPG Towing? Then what am I supposed to be getting unloaded? Because that's what I get unloaded.

I'd totally expect to get like 5 MPG towing.