aftermarket ones are JUNK,PERIOD....... A couple of years back a buddy installed one in his bro's silverado,gives me a call and says still having the same problem,thinking he install a o.e.m pump.i said well lets through a fuel pressure regulator in it,also common problem on silverado's,gotta be one of the two.so we pulled the intake [WAS A CFI} injected truck and installed the reg,all back toghether and i take it for a spin,SAME problem again.
i go don't tell me you put a aftermarket pump in this thing.YUP,sure enough.got him an o.e. pump.he installed it the next day and i get a call problem solved.all that extra work dropping that tank for a second time plus putting in that reg,all for not-a.
seen it time and time again,not saying it's a sure thing but i would start there.
GOOD LUCK WITH IT,HOPE IT WORKS OUT.
Dave..............