Don't kick me out for saying this guys, But I'm not brand loyal to Ford or GM. I've had the 2004 7.3, 2004 6.6 Duramax, and now the 6.0(2006) all on the same basic truck(4x4 crewcab dually automatics). Here is how I've observed the milage thing(hwy speed is 75mph) --Duramax--hwy 21.2 city 17.4---7.3ps--hwy 16.2 city 11.4-----6.0ps--hwy 15.8 city 11.1. I don't tow anything to answer that question( I know why dsl then.......resale and addiction to power I guess). The 6.0 just seems a littled labored compared to the other 2. This is all for what it's worth. I guess to wish for a 7.3 with a 5spd auto. Later guys.........

 

My 06 F250 6.0 PSD will go from Hays Kansas to Cheyenne Wyoming on 1 tank of Diesel Fuel (35 gallons). I set the cruise control for 70 mph (75 when I hit Colorado), make turns for 2K RPM............Thats all there is to it.

Gunner15a
Better Living Through Superior Firepower

 

My experience is similar to FSeybert. I just returned from ~4500 mile cross-country (MD to AZ) towing 6000# going 70-44-40 route there and coming back 10-20-77-81. My mileage before I left was 13.7 with avg ~37mph calculated. I set cruise at speed limit for wherever I was & always fill the tank up the neck. I averaged 10.6 mpg for the trip. I noticed that the lie-o-meter is actually pretty close to my calculated mpg's. While out in AZ, I completely unloaded the truck of all the crap I carry around and drove 40 hwy miles to Mom's. The lie-o-meter showed 19.4! I am a firm believer that the miserable mileage I got before the trip is a direct result of moving a lot of bed-weight at slow speeds. When I empty-out and speed up I get much better mileage. I also noticed that I got the best mileage at 60-65, and as I sped up to 75 my mileage would drop by 1.5 - 2.

Seems like the only way your Pop will know for sure what the issues are, is to do some controlled testing, i.e., do a baseline calc the way you're set up now at normal 80 mph, then back off the speed to 60 for the same run and compare. Then take the chip out and repeat the 80/60 runs and compare. That should give you an idea what is going on.

 

Sorry I should have quantified this a little bit before I posted it. This is with the the truck unloaded, not pulling my trailer. Now, with my trailer on (it's a 2000 32' Jayco Designer w/3 slides) I can go from home to Jal NM on 4 tanks of fuel.

Gunner15a

 

06 F250 excab short box got 19 by hand unloaded at 60mph and got 17 on the way home at 65-70mph

 

I have to agree with Deluxe05 in that the larger tires are making a bit of a difference as well as cruising at 80mph. I made the change up to the stock 20"s and cruising at 70mph I noticed a drop of about 2 mpg. I'd recommend having your dad either slow down so that he's not over 2000rpm or tell him to just grin and bear it!! My dad complains about his 05 GMC Duramax because he only gets 14.4mpg, but then that's because he drives 80-85mph on the highway! I drove his truck at 2000rpms one weekend and got 19.7mpg. So all I'm saying is that you'll have to pay for driving faster in a heavy truck due to physics no matter what brand the truck is. Just tell him to slow down if he's not happy.

 

If your dad is looking for mileage and saving a buck ask him how much that new Duracrap is going to cost him over the current truck and figure how much fuel he could buy with that money. If he's that worried about MPG dump the 7800# brick and buy a smaller truck or car?
Just my 2 cents

 

My dad is only complaining about the mileage of his truck because my brother and both have diesel trucks and we get alot better mileage than he does. My brother even follow my dad one time going the same speed from Sheridan to Gillette in his 6.0 CC 4X4 and was getting almost 17 mpg. Thats why I am wondering why there is such a difference. I talked him out of getting the Duramax, he is going to keep his truck for a while and look into the new 08 after a year or so. Make sure they work all of the bugs out of it first. Thanks for all of your input on this subject everybody.