Just bought this used 03 dodge with about 150K on it. Was running great, then the other day I noticed that when you depress the pedal more than about 1/3 down (especially on a hill) it stumbles, looses power and just acts wierd, the sound totally changes when it happens, like it is starved of fuel.
I replaced the fuel filter this afternoon, checked the APPS voltage... took it for a spin and at first it was back to normal.. then after about a mile it started surging or stumbiling when you depress the pedal....
The codes are 0483, 0602, 2509. I do not have any mods on the truck but the previous owner has some kind of power chip installed I think, there is velcro left on top of the fuse block like something was installed there.

Any help on this? Could it be a bad lift pump?
Thanks