I have a 98 ram 4x4, auto, 5.9 with 150k. It has seemed to have slowly lost some power over the past year and now after driving on the highway for a while when I get to about 3000rpm it starts to stumble. But when I let off the gas and let it shift to the next gear it is fine till it reaches 3000rpm again and it starts to stumble again. I put a low temp thermostat in last summer because of overheating problems but I don't think this is the problem. I am guessing fuel pump, fuel filter or injector problems or maybe even cat converter. Any ideas would be much appreciated. Thanks Also I've done a vacume and fuel pressure test and everything seems fine.I've also done an air induction service.
The problem has been fixed. It was a clogged cat converter.
May be a carbon issue, IT is good maintenance regardless if it fixes your problem, try an air induction service and see.
I would try what I call an air induction service.
I like to use castle hydroblast. You spray it into a vacuum line such as the brake booster line if nothing else is accessible. Full spray for 3 minutes, stall the engine with it or have someone kill it while your spraying. Let it set for a few hours then take for a short drive in low gear, revving the rpms to help break it up. First use Castle cleansrite to clean the throttle bore. Try to get the throttle plates scrubbed good with a brush, while your spraying. Use a rag to wipe the carbon out between brushings. Seafoam is another good product, but smokes a lot.
IF you can't find Castle, here is my rep's email: robw@castlepackspower. Com