This car was running smoothly but it lacked power. We found low compression on some cyls. The engine was pulled and a local shop rebuild it. The engine has much better power now, but the issue is this: At idle, the engine is running smoothly, but shift into drive and the car starts shaking. It wasn't shaking before the engine was removed. The transmission and torque converter were not removed when the engine was pulled. When stepping on the gas, applying power, the shaking is not noticeable. It's just at idle that it is really noticeable. A whole lot of shakin' goin' on. The transmission is the 3 speed automatic that starts out in 2nd and has no overdrive.

Any thoughts on what could be causing the shaking?
We're trying to figure out if it's the engine, once it is under a load when shifting into drive, that needs an adjustment, or is it the transmission or torque converter.
Thanks.