Ok, I got my 4.10's installed, and I was told not to shift rough or launch rough for about 500 miles, which I have done so far.

Well it's been about 200 miles now and today on the highway the car was shaking like a bitch in 5th and 6th gear, and I couldn't even hit 70 mph. Is this normal?? Is it cause I haven't got my speedo redone yet? Are the gears still breaking in?

 

Sounds like you got the old vibeshaft. Get an LS1 or 1Le. Should fix it.

 

cool, I just ordered a 1LE. Hopefully this fixes it.

 

The "break-in" period is an interesting concept. Why would new gears need a break-in period? When you buy a new car, the gears haven't been pre-broken in as far as I know.

Seems like if the gears are set right you should be able to drive it like you stole it from the get go.JMHO.

 

Bubba sounds right but they all state break-in required. That vibe will tear up your pinion bearing which will change your pinion depth which will jack your gears. Good luck, in retrospect I would prefer 3.73 over 4.10 just to save the vibes and noise.