1997 C 3500 Eprom And Timing?

[PineApple Express]

Ok I have a 1999 C 3500 with a 7.4 (454) it has about 64K orginal miles. I have towed several trailers from open car trailers to my current 48 foot enclosed trailer about 12K total weight. I purchased the truck as a second owner from a dealer. It run very good with no load. With load on it and climbing a small rise in 3rd gear the power falls off fast and does not want to shift to 2nd. If I continue to try and push the truck it will toss a code "Random engine misfire" I have changed the plugs, wires, dizzy cap rotor, the fuel pump was making noise so I had it changed, it has new injectors on it too. I also found the rotor out of time and I am aware that the computer controls timing. I found some where in this forums there was a GM prom update for towing heavy trailers. I called a local GM dealer and they said there is no Eprom update as well as no way to set inital timing. Is there anyone who can tell me what that prom update is numbered and can the base timing be set with the truck running? The air filter is also clean. Everything is stock factory. I checked and replaced the FP regulator, the ignition module in back of the intake, replaced the MAP, TPS and cleaned the MAF too. One thing I do notice on cold start up it starts to run on a rise idle and tried to die off. I did veryify the fuel pressure and it is well within spec's for this truck. ANy help would be appreciated for this sick 7.4 vortec that is running nutered.

 

 

Thanks

 

Chuck

PAE

[496sixpack]

I am new to this forum and noticed your posting. I have exactly the same issue with my 1996 C3500 dually. Just hit 100,000 miles. Runs good empty. Uses no oil, everything seems to be right as rain except no power. When pulling my 7000# car hauler, this thing is a total pig. My 2006 5.3 powered 1500 actually pulls it with what seems to be more power. I have even been thinking about dumping the TPI in favor of a carb, but I don't know what effect that would have on the 4l80. If you figure yours out, let me know.