Hi - We a have a 1996 Dodge Ram 2500 Cummins 5.9 L Intercooled Turbo with a 4 Speed automatic transmission. The Dodge dealership in Auburn California recently upgraded our software with PCM 04886426. Since then our mileage has decreased significantly from 17 to 15 unloaded and from 13 to 10.5 when pulling our 5th wheel. The guys at the dealership are saying that no way the software upgrade could have caused a MPG decrease and they say they can't put it back. The software upgrade was installed to correct gear hunting at the 40-45 mph.
Does anyone know what we could do to get our mileage back and what we could do to prove to the guys at the dealership that we're not crazy?? We really want them to fix this since they assured us that if anything our mileage performance would increase with the upgrade that cost $200 plus.

 

I'm gonna have to side with the dealer here.
The pcm on your vehicle has very little to do with the engine.
The fuel system is fully mechanical and has very little computer control.
I would get the injection pump timing checked by a competent diesel shop.
Is there any loss of power or other driveability complaint?
How many miles on this engine?

 

I agree also; the 12-valve Cummins in your Ram is not controlled by the PCM. It's totally mechanical. There is no way that a PCM flash would cause the MPG decrease.