I replaced both transfer/main fuel pumps and main still whines on 1993 Volkswagen Cabriolet

I originally put new main pump on which started whining after a week of driving and got hot and quit. I just replaced both transfer and main pump and after idling about 10 mins the main pump got hot and started whining. It will go away after a few seconds and pump will cool then start heating up again and whine. I replaced both pumps with quality parts. I don't know where to go next

Check wire connections at the pumps, got to be clean and tight! Car running ok?
Car runs fine. I'll check connections. I checked plug at fuel pump and it's fine. Put a new gas cap on and oem filter. Just ran it and main pump is still getting hot. I did check flow on new transfer pump and is well within specs. Any ideas would be greatly appreciated

Good news the fuel pressure regulator was bad.