Engine/Transmission (1998.5 - 2002) Transmission Slipping???

[pparker]

I have a 98. 5 2500 w/about 70k miles on it. When running about 55 mph with just enough throttle to maintain speed, the engine rpm will jump up about 200 - 400 rpm and then right back down. It will keep doing this every several seconds. If I give it more throttle, it does not do this.



I tried searching the forum, but couldn't find anything that sounded like this.



Any ideas what could be causing this?



Thanks,

 

[Big Rich 01]

could be torque converter lockup going bad

 

[VolsFan]

my auto transmission did the same to me, thats when i decided it was time to get her rebuilt, plus I wanted it to be able to handle some power mods later on down the road. I still have a single plate t/c, just a lot bigger than stock, transgo shift kit, bd valve body, and kevlar bans. The truck shifts like a dream, even full throttle doin burnouts the transmission has held up like a champ, and i know i'm rough on it, I just like the peace of mind knowin it will handle whatever i throw its way, as long as I watch my temp gauge, haha

 

[JNobach]

My 98. 5 was doing the same thing, even worse when it was raining. I cleaned the grounds; especially the one on the front of the block by the thermostat housing and the problem was solved. Might be a start.

 

[KTobin]

At 55 MPH, on steady load and steady throtle, you should be in full lockup. A 200 rpm repetative drop sounds to me like your tourque converter locking and unlocking. This has been well documented by many here and a search under tourque converter unlocking should give you an evenings read. The most common cause of this condition in electrical noise in on a sensitive PCM. Clean ALL your grounds as mentioned in this thread, and use a dialectric grease to protect them. Once again, your search will reveal what many of us have done to memedy this condition. If all this fails, a noise filter may be needed. Although you may have a worn or "noisy" spot in your APPS/TPS at this throttle position as well, I'd stick to the inexpensive fixes first.

Kevin