Just purchased a 2000 Formula Fastech 312 twin 454s bravo drives, boat pulls hard to left at cruise (40mph) when you release steering wheel. Any idea why? (new to twins).

I had a boat that did that at one time. It had a small leak in the Hydraulic steering. When that was fixed no more problems.

If you have cable steering, maybe check the tow.

I assume your drives are rotating in opposite directions and you consequently have left and right rotation props on it correct?

yes, check the drive toe setting, ext steering ? if not the p/s control valve could be bad as well...