Hello all! Just purchased a new factory stock GM Good wrench engine and had it installed at a local shop. My problem is with vibration while under acceleration. Engine runs fine at idle and while cruising at a steady speed. As soon as I hit the gas the vehicle starts to vibrate. Please note: Prior to replacing the engine I did not have this problem. As far as I know, the new motor came with a harmonic balancer. The shop that installed the engine did replace the clutch assembly and flywheel however. While at a complete stop with the transmission in neutral; I rev the engine up slowly while watching the tach and checking to see when this vibration starts. It appears to start at approx 1000 rpm’s. It will then go away shortly and return at about 1500 rpm’s. It will then start to vibrate again and then go away shortly .thereafter and return. If I had to guess; I would think it was the flywheel/clutch assembly that was out of balance. Any and all suggestions would be greatly appreciated! Thank you!