Anyone experience any problems with the Durmax after the install of a chip or programmer? I have the Bullydog programmer which performed well at first........now has very poor performance. Pulled it out, changed fuel filter, air filter, tranny serv., etc. and it does not run like it should at stock either.....no low end throttle response or power. Have took it to 2 different dealers and they find nothing with the diagnostics check.

I've lost around 2 MPG and a little power but mine is totally stock except tire size. I was told by my dealer that it's the ultra low sulphur diesel fuel. They've taken out alot of the lubricating components over time and now the sulphur. This could easily explain it but I'm not sure. It's funny that you mention this though because I have lots of associates who have diesel pickups and most of them are saying same thing.

From what I have been told, no expert though, is that there is an inherent 3% loss in btu's with ULSD, which equates to a power loss. However, refiners are supposed to be adding something to correct that. With the reduction in sulphur there is also a reduction in ash which did added some lubricity. Refiners supposedly taking care of that as well. To be honest, I have an 05 Duramax and just made a pull down the coast and my mileage didn't change noticeably.?? Maybe someone from the industry will chime in and bring us up to speed.

I use RBP (Rolling Big Power) Additive and all works great w/ using the BULLYDOG CHIP 07 dually Chevy

A friend of mine had the same complaint,the dealer tested his fuel,it had a real low cetane rating (below the oem's minimum),he quit buying cheap fuel from speedway and admiral stations and his mileage/power returned. I too have a duramax,its winter here though,the winter blend fuel,extra fuel ecm dumps into the motor to make up for low ambient ,extended warm up times and my taller winter tires kill my power and mileage (tires are 10% bigger,mileage drops 25-40%),Smitty

Back to your problem though,go on the diesel page and browse the forums,you'll probably find your answer somewhere there,Smitty
http://www.dieselplace.com/forum/index.php?

I always try and get Irvine fuel for mine when I can.

Have the programmer checked...I have a Edge with Juice and LOVE IT!!!! what Year DMax?

Keep in mind that the transmission has been "learning" how to shift with the extra power.... when you return to stock, it doesn't know when to downshift and has to "re-learn" how to put the power down to the ground.