Tow haul has no control over the engine , only the trans.

On that note, hell my setup gets 16 on the highway. Close to 6k lbs, Awd and 4.10's. I turn 2400-2500 at 75mph.

 

I agree, that's damn good mileage - especially for a heavy truck. I'm getting around 15.5 from mine, mixed driving.

 

Hell im in a crew with pipe bumpers and 4:10, when the original motor was stock it never got over 12mpg and i have owned it since new over 300k (oh and its 2wd) a couple other guys i know with the same trucks get about the same.. I only wish i could see 15 mpg out of mine,

 

Its a .040 over 6.0 but the trick is higher compression makes it more efficient plus with damn good exhaust system and good heads and a matching tune you cant go wrong. I too have HP Tuners but by no means can I claim to be a tuner. Maybe one day. I do live close. I'm in Friendswood. I used to work in Deer Park but thanks to the recent strike I have a bunch of time on my hands. I pulled my rear leafs yesterday to install a set of CalTracs today and if all goes well, plan on going to Baytown track tonight to take advantage of this great air!
I have owned my truck since new as well. 2003. I only got 10-12 mpg on the hwy and 8-10 around town stock...

 

Well 10 months later and I finally got it right! Runs like a beast.. Thanks to changing to 8.1 liter injectors and SXT Performance for tuning it and de-sensitizing the knock sensors!!
most tuners don't sit there and help you trouble shoot but they had no problem and worked with me for hours this Saturday on and off the dyno! Located in San Leon just down the road from me..

 

Good deal man! Its always nice having having people who are willing to work with you until your satisfied. I did my engine swap myself and only had someone else tune it. That way you know its done right. Glad to hear it worked out for you.

 

Good to hear, why did they have to desensitize knock sensors?

 

He said everything was tuned properly (first I had a guy in Pasadena tune it then HHP/Chucks Tuning done) and then SXT and he said it was setup close to okay but no matter what everyone of them had knock sensor trouble. EVERYTHING IS NEW including knock sensors and harness they are simply just too sensitive?? Thanks fellas!

 

Did you do a dyno tune? If so what kind of numbers did it pull?

 

Wow nice to see someone else get this figured out. I have almost exact situation. I have a 02 2500 hd with 325000 miles and did the atk swap last year and have had the exact problems you described, no noticeable power increase, stumble at about 2300 rpm, check engine lights blah blah blah. So what all besides the 8.1 injectors did you do to get it running like it should?