My dad owns a 99 ram 3500 4x4 with a Cummins in it with an auto tranny. Truck has over 150,000 on it. Here is what it was doing. We were taking 2 trailer loads of horses home from the local fair grounds which is about 35 miles from home. On both trips down with the trailer loaded and the one unloaded the truck did it. Trailer is a 4 horse gooseneck with a front tack room, and the trailer is steel. Probiably close to 6,000 lbs empty and loaded fully 10k plus. Noticed that the truck seemed to jump and shutter like you were slipping a manual clutch vehicle with a warped flywheel or pressure plate. It would do this when the power was applied and the RPMs weren't up above 2,000. It was much more prevalent with the Torque Converter locked but it would do it with or without it locked. Manually kicked it down to different gears to see if it was a possibly the engine stumbling. Engine fueled up to about 18 lbs of boost with no issue when it wouldn't slip. Would seem to do it in multiple gears but when the engine was lugged at lower than 2,000 rpms with the boost up. Could power through it if you make the converter unlock or the tranny downshift and get the rpms up. Grudgingly knew that we had to go pickup my Mom's camper this morning which is a 32' 5th wheel. Knowiing it was doing this we were looking for it and tried to pamper it just so we could get the camper home and then address the transmission issue. Well it didn't do it a lick today at all. Last night pulled the dipstick and the fluid seems alittle foamy and smelled burnt so I'm pretty sure it was slipping. I just can't figure out why it wouldn't do it again. The weather last night was just plain old wet. Today it's cool but sunny and things are drying out pretty quick. I'm wondering what would cause this? Unfortuately it's a 99 so the on-off on-off key trick won't show any trouble codes on it. Gonna put a filter in it just because but I don't think it's a fueling/engine issue. Any sensor on the tranny that is a prime candidate to cause this issue? Thanks.

 

sounds a lot like a torque converter on the way out. I'd probably change the fluid and filter. I'll suggest you go with atf+3 or +4 for the fluid. I know you can use dexron, especially if it's a built (performance)trans, but since it sounds like you have a stock trans I'd stay with the +3 or +4 stuff for now. It may be too late, once the slipping starts, it's only a matter of time before you have to have a rebuild done.

I'd also do the band adjustments while you have the pan off, I probably won't help the issue your having but, it won't hurt either. You might be able to extend the time before rebuild by keeping the rpm's up while towing and not towing in overdrive.

Jeff.