Hi all, thanks for taking the time to read my post.

I have a 1999 GMC Suburban C2500 that drives quite well around town. The only problem is when taking it out on the highway; around speeds of 70mph or higher, it will occasionally buck forward and back, a bit of a violent jerking motion at times. I once thought it was going to die on me in fact.

Any ideas? I paid a mechanic $500 to replace the fuel pump almost 8 months ago, because the previous owner said it would need one. So I'm really hoping the mechanic did his job and actually did replace the fuel pump.

I checked the transmission fluid. It goes past the operating window where it says "HOT", so it might have a little too much fluid, and it's also mostly black (no red color). Would that have anything to do with it?

It's weird because it runs just great around town, it's only at highway speeds that it jerks around a bit. Maybe a fuel filter?

Any ideas would be great. Thanks.

 

Transmission fluid should be red in color, not black. Smell it and see if it smells burned. I would highly recommend getting the transmission serviced first (fluid replaced as well as filter).

 

Probably looking at overhaul in near future. Transmission is slipping. That's why the fluid is turning black. Too much heat being generated.