slight vibration under power when driving

Hmmm.... Alignment nor engine mount are likely problem areas here. I’d definitely start with rebalancing to tire. If still shaking rotate to rear to see if shake moves. If so, you have a bad new tire bead; if not probably a bad new axle. Also could be a bent wheel, so check when rebalancing. New axles have a fairly high failure rate, as do new wheel bearings...especially if hammered in or overtorqued. Good luck.

Had an alignment and had the tires re balanced. rides like a new car thank you very much.

Realignment was probably unnecessary, it sounds like you had an unbalanced wheel. Sometimes new axles need to break in too.