1990 Pontiac 6000 car will only idle

Pulled the fuel pump and tested with voltage pump seems strong have put 2 computer boxes from j-yard in but it pops when I turn the key, idles a while, stalls when I try to give it gas definately getting spark to plugs could this fuel pump sound good but not be delivering right pressure? Could it be a regulator this is a 3.1 multiport motor how or where do I check fuel pressure- also I did put a new fuel filter on before pulling pump ran good 2 wks ago then just quit seems like a fuel prob. Any sugg. Would be appreciated