I own a 1998 Dodge Ram 2500 w/ 24 valve Desiel engine. When I am driving it and it gets about 45 mph plus it acts as if it wants to idel up and down. You can feel it and see the rmps moving up and down. I let my foot off the pedal and it stops doing that. Any suggestions on what it could be? I just bought this truck used a week ago.

 

A buddy here had one do that and his lift pump was going out or was out.Check your fuel pressure.