[PxTx]

I think you are right about the fuel. That pump may be okay if the inlet is unrestricted. Sometimes filters, the size of the inlet line and such can cause a decent pump to become starved. Running at least 1/2 tank could help a bit. How large is the inlet on the pump? If the 120 gph is with a 3/8th line and you have a 5/16...well you get the jist.