Hi, recently swapped motors to a built 5.3 with a Borg s480, had the car running well, had done 150 or so ks, when it developed a low rpm high load miss, it was clearing up but not any more and breaks down under any load.

Found loose battery terminals and the cam sensor unplugged 🤦🏼*♂️ Fixed both of those but still not happy, have compression tested as well as put my spare coils and leads on as well as new plugs, spare crank and cam sensors
The car has a gm 3 bar map sensor installed.
Reluctor is tacked to the crank so shouldn?t have moved.
Any help greatly appreciated