98 2500 4x4 68K original Automatic. Going up the mountains pulling my trailer, as soon as it shifts to 4th gear at 45 mph, the truck will make a popping sound and buck a few times. It will continue to do this until it gets to 50 mph and then nothing. I noticed a lot of black smoke coming out of the exhaust when it is doing this. If it were a gasser, I would think that it is misfiring. It really only does this when it is under a pretty heavy load. Any thoughts?

 

I don't know what it could be but I'd recommend you turn O/D off when pulling especially when going up a grade. It's not good for the engine (lugging) or tranny.

 

you're running out of fuel, change the fuel filters and pre-filter if you havnt yet.

 

Where is the prefilter located?

 

down next to the lift pump.

 

Check out www.dodgeram.org. You'll find instructions for lots of stuff there.

 

Try this http://dodgeram.org/tech/dsl/filter/pre-filt_clean.htm