when i floor my 88 iroc-z it jumps it's almost like someone is hitting the underside of my car with a brick...you can feel it in the gas pedal and hear it....it shifts fine between every gear this is the only problem i have ever had with it....does anyone have any clues?

 

check your trans mount,sounds as if its broken

 

Trans mount absolutely.

Very cheap part, not that hard to do, need a floor jack and a piece of wood to support the pan. 4 15MM bolts on the outside, 1 13?? mm nut on the center bolt (if yours is even still there, mine was gone.) then 2 13MM bolts holding the mount to the tranny. You'll be replacing the rubber bit that those last bolts hold to the tranny and it includes the center bolt.

Greasy, very easy job to do with the right tools.