The IRF3205 is a better option. After removing the FETs, I'd suggest checking all of the gate resistors for the PS FETs. I generally replace all 8 of them.
Before you do anything else (including ordering parts), I'd strongly suggest that you reas as many JL 500/1 threads on this forum that you can find.
Before you do anything else (including ordering parts), I'd strongly suggest that you reas as many JL 500/1 threads on this forum that you can find.