I just got running a 95 cummins with the automatic transmission. I purchased the truck last july and it sat in pieces until just this past week. THe engine was bad when I purchased it and I did a major oh of the engine myself. Drove it to work acouple of days and everything seemed to be working fine. Friday nite I hooked it up to my 28 foot fithwheel camper and noticed that at 60 mph the transmission is either slipping or the torqure converter is locking and unlocking. The puzzling part is that it only does it on a rough stretch of road when the truck is jerking around. This leads me to thing that my problem is in the valve body. If I am driving 60 mph on a rough road and I leave my foot on the throttle in the same spot. While watching the tach the engine rpm will go up 2-300 rpm for just a second and then come back. The engine does the same at 55 and 70 mph so speed seems not to make a difference. So I am wondering if I have a torque or a valve problem or is it just from the trans sitting for about 8 months with no use and maybe i need to add some sort of trans addative. I have just installed a extra oil cooler with a eletric fan and a new filter and service.

 

Check ALL of you grounds. Engine, Transmission, Frame, ect. I'm guessing you have a loose/dirty one somewhere. It's a fairly common complaint. Checking and cleaning your grounds is free, so start there.

 

check your brake pedal and make sure its not loose enough to set your brake switch off. mine did the same thing when i hit a bump. just put ur foot under the brake pedal while goin down the road and hold up on it and see if it still does it. if not check your tps.