This has turned into quite a helpful thread. I am usually at 50-60 miles by three quarters of a tank as well and 175-200 at half a tank. My best tank had me at 330 miles in between half and a quarter if I remember correctly.
I know the 4.30's are not optimal for fuel mileage, but I would not trade them. I can set the cruise at 70-75 mph and it will not downshift out of OD on any hill around here including one particular hill that is not necessarily steep elevation wise, but one of the larger ones around here. My wife and I bought a new 2001 Dodge QC 318 4X4 with an auto and 3.55's. On this particular hill, that POS would go right to second gear at 70 mph to maintain speed up that hill if left on cruise control. That was my last Dodge.

 

I second the tire pressure. I have the 6.0 and was getting about 14 around town. Seldom if ever was it on the highway. I had the tires at 55 psi. last year I took a trip up to GA and aired them up to 75 psi. I got 22 on the highway and now get 17.5 around town. My point is that tire pressure makes a BIG difference.

My ex only has 25k on it so it's just getting broken in.

 

See, I keep telling people that rolling resistance makes a huge difference.. not just tire pressure but the type of tire Highway tread vs AT vs MT etc... rotational weight of the tires make a big difference too....
Michelin Xone semi tires are a great example Michelin Americas Truck Tires X One® Tires Page

 

Don't feel bad, we all started somewhere with these trucks...

IAC stands for= Idle Air Control Valve.

I'm not sure where it is on the V10, but on all the other engines I worked on it's on the intake manifold (or the part where the intake connects to the engine): two bolts secure it to the manifold and it has an electrical plug going to it. Hit it with some B12 Carb Cleaner (aerosol) and the majority of the carbon and gunk will fall right off. Soak the part that goes to the intake in some B12 for an hour or so, then spray it down with some brake or electrical cleaner to get the B12 off, let it dry completely and you're done.

To run SeaFoam into the intake, drive your truck until it's at normal operating temp, have the open can of SeaFoam closeby and with your truck running pull the hose off the Master Cylinder and put your thumb over the hose so your truck doesn't stall. Slowly induce it into the intake (they say usually half a pint does it) and shut your truck off. Give it about 5-10 mins and start your truck again, rev to about 2,000 rpm, and watch the smoke fly! Once the smoke goes away you're done...I also change the oil right after this too. Not something you have to do, it's just what I do...

As far as adding SeaFoam to your tank, I don't notice much of a difference either; that's why I use B12 in the tank, it's way more potent and makes a noticable difference. Seafoam's place is in the oil and intake as far as I'm concerned.

 

ill 3rd the tire pressure issue my 315 bfg's were down to 20 psi ! momma hadnt complained all fall she just kept filling her up... finally we took a family trip and i was shocked at the mpg's we were getting pulled into gas station after 300 miles ....... i picked up more than 3 mpg's airing up to proper levels cheapest mod ive ever done

 

Something else: NEVER go by what the sticker on the door says; especially if you have load range "E" tires. Even though it's obvious you have aftermarket tires on, some places will still inflate to what's on the door and not what's on the tire, causing premature wear and other failures.

 

Yep - it's on the rear of the intake at the throttle body. Remove the plastic cover over the throttle body and you'll be able to see it back there. It bolts up with the 2 bolts as Red says and then has an air hose which runs towards the driver's side and then forward to the air intake. You really need to remove it to make sure it's clean. It's fairly easy to do - just be careful to not drop the bolts.... took longer to find one of those then the entire rest of the job! BTW - the hiding spot was the valley under the intake - a flexible pickup was my friend that day! My IAC was actually dirty enough that I cleaned it and then replaced it when a rough idle wouldn't go away. The problem was the plunger would not move freely even after cleaning.

 

The dealer had my E tires at 45lbs so I aired them up to 65lbs. They are rated at 85lbs max. Is that enough? I did not notice much of difference in gas mileage but the ride was rouger.

What other reasons for Ex to use a quarter tank for first 50miles then 150 for next quarter tank? I thought I had a leak or something. It does not make any sense. Does it????

 

That should be sufficient air expands as it gets hotter (you driving down the road) so it should euqate to a decent tire pressure. You won't notice the increase right away, but you will over time.

Your fuel problem may have been a batch of bad gas and the fuel injector cleaner they dumped in the tank as part of the cleaning may have freshened it up to where your mileage improved.

 

This is actually still happening. Even after the fuel injector cleaning. I have been through 3 tanks since then and no matter what I do. Drive nice or crazy I get 50miles for the first 1/4 tank.

 

Maybe it is the way the gauge works. When it is at 3/4 of a tank fill it up. If it takes 11 gallons then you know the gauge is on. However, if It takes 5, then you know it is just the way the gauge works and your mpg's are fine.

EH

 

Interesting idea. I never thought the gauge would be off. I will try it.

Thanks!!!

 

That's kinda what I was thinking too, not sure what the proper name is on our trucks, but on an ATR 42 and 72 they call it a "Fuel Quantity Indicator".