First off, the car is a 89' Iroc, fresh rebuild 350, all stock, tranny is the 700r4. To my understanding the tranny had been replaced by the previous owner.

At around 55, the car will start to shudder a little bit, but starts to shudder worse the faster you go. It shudders whether you are accelerating or coasting.

Possible symptoms?
Wheels balanced?
Had new tires put on last year, they said they balanced them, can you trust Tires Plus?
TCC?
U-Joints?
Driveshaft?
Any other ideas for this?

Also, another symptom, don't know if it is related or not, but when the car is cold, the car shifts real good, but when the car has reached operating temperature, it does not shift very good. Under casual acceleration, the car will very quickly shift from first to second. Under hard acceleration, the car stays in first up to about 4500 rpms and then shifts, but when it hits second it is like I have a big loss of power(very sluggish feeling) until it gets up to around 2500 rpms. When the car is cold and I go WOT from a stop, the tires break loose. But when the car is hot and I go WOT from a stop, I cannot break the tires loose.

Oh, and when I am coasting at any speed and kinda jab the throttle I can hear a clunk from the rearend...

You guys got any ideas at all?

 

Are you sure it's from the rear, and not underneath you, sounds like the tranny mount is broken.

 

hmm, good idea, i'll listen closely next time I take it for a drive.

 

i've got a similar problem on the same section of this board. I don't think it would be a trans mount or T arm bushing cause i replaced those last summer. I can check them for tightness cause I have a vibe....we'll see...