Alright, here's the deal...if I get on the freeway and put it in 6th gear, (under 70 mph) the engine shakes pretty bad. It kinda has a knocking sound to it. It runs great when I get the rpms up over 2500. What I need to know is when you floor it in 6th gear what gets stressed that could cause the shake? Is the clutch stressed in this situation? I'm thinking it might be the clutch because in addition to the problem listed above, after being in stop and go traffic, it seems like it's trying really hard to accelerate from a stop. The clutch has about 30000 miles on it

 

you should NEVER be flooring it in 6th, that's lugging the engine and possible causing it to detonate. It'll shake horribly.

If you want to floor it, downshift.

 

Also hard on bearings, clutch should have nothing to do with it.

 

I never actually "floored" it in 6th, but giving it a considerable amount of gas causes it to shake. It seemed to do this after the heads were milled due to a blown head gasket, I'm guessing it bumped up the compression a little bit.