Fuel Pump keeps burning up on 1993 Isuzu Trooper

I have 2 93 Isuzu Troopers. 1 automatic over 150,000 miles. 1 standard over 60,000 miles. Both SOHC and 3.2 L engines. The fuel pumps keep burning up.

Things we've done:
Replaced pumps
replaced filters
cleaned tanks
cleaned injectors
hard wired pumps ( the automatic hard wired still works, the standard does not)
changed spark plugs and cables
replaced all parts for timing
new batteries and terminals
checked all fuses

We are lost. The only thing we haven't done, replaced fuel lines. i need help. Can't figure this problem out. Oh and have gotten the pumps from different places.

Asked by for the 1993 Isuzu Trooper
I'd try an OE Isuzu pump. There are lots of low quality parts in circulation. Different chain stores could sell the same bad part in their own box. I'd also replace the fuel pump relay.

Actually the pump is not from a chain store, but OE is an idea. As for the relay, it has nothing to do with this situation. The pump is hard wired, meaning It's wire to a switch that has a direct feed off of the battery. We are actually thinking it may have something to do with the vehicles wiring. I was hoping to find someone who has dealt with a similar problem. ~dolly9803~
Could you tell us how is it hard wired? Is it hooked up to the ignition switch?
Anyway, did you remove , clean and re-tight ground connectors?