it just started today, i recently purchased a 95 z28 with a six speed, heres the prob it shakes like crazy when on the highwayin 6th gear gets worse when i give it gas in 6th, i feel it stumble and shake some in every gear except 1st but the worse gear is 6th, it doesnt shake while idling or if i rev up the engine in neutral it still doesnt shake only while driving .. oh yeah theres no ses light on either, am i having trans problems or engine problems

 

I would check your U- joints on the driveshaft

 

What should i look for. And why the u joints just trying to get a better idea

 

I would check your plugs and plug wires very carefully. It sounds like a misfire problem.
Any noises? Usually U-joints that are on their way out will make clanking noises when torque is applied.
This ONLY happens in 6th gear?

 

yeah mine does the same thing, but only on decel in 6th gear. and its mainly over 70mph. i can go over 70 in 5th and decel and no vibration. just 6th gear. its innoying, hope you figure it out.

 

Have a stock driveshaft on it? There is a TSB somewhere out there (sorry i cant pinpoint it right now- ya oh soo helpful i know), about vibration caused by an unbalanced driveshaft i believe?

 

Vibrations could be caused by a number of things in your drivetrain, alignment, crank dampener, etc. Stumbles however are likely to be caused by you ignition, check plugs, wires, coil, opti, etc.