95 chevy z71 spitting and shaking at 70mph
 

I have a 95 Chevy z71 350 and a couple of months ago on the highway it started shaking real violently at 70mph, and kinda bogs down and wont go any faster. If I let it coast for awhile it will go away and i can climb back up to 69mph. If i put my foot in it it will spit out the tail pipe.
Parts iv'e changed:
Fuel pump and filter
EGR valve

I don't have catalytic converters so i know there not clogged.
I thought fuel but I don't know its got me buffaloed
Any help would be greatly appreciated i just don't wanna keep throwing parts at it.
Thanks

hmm.. maybe its a spark issue?? hard to tell without seeing. is that an efi engine or tbi?

My friends truck had this problem but not as bad. He has a '94 GMC Sierra and all we did was change his plug wires and it fixed the problem right away. But that's just my guess is the wires.

camaro820- its a tbi motor
bravelil305-the spark plugs and wires are not that old but i will check someone also told ecm so i will be checking this weekend
thank you for the advice