99 GMC Yulon fuel system problem

I have a 99 GMC Yukon. Back in Nov it wouldn't start so I carried it to my mechanic. The fuel pressure was low so he replaced the fuel pump with an AC Delco pump and tuned it up. Last monday it wouldn't crank and no hum from the fuel pump so I carried it back It cranked fine for him but he replaced the pump and went with a Bosch pump. Yesterday it wouldn't crank again also no hum from the fuel pump. Back to the mechanic and it starts fine. Any ideas what the problem could be?

I have a 99 GMC Yukon. Back in Nov it wouldn't start so I carried it to my mechanic. The fuel pressure was low so he replaced the fuel pump with an AC Delco pump and tuned it up. Last monday it wouldn't crank and no hum from the fuel pump so I carried it back It cranked fine for him but he replaced the pump and went with a Bosch pump. Yesterday it wouldn't crank again also no hum from the fuel pump. Back to the mechanic and it starts fine. Any ideas what the problem could be?

Check all grounds.

Check ignition switch.

Next time fuel pump is not operating run a fused test wire to fuel pump to see if it operates then.

Nevermind, problem solved. loose wire nut on wiring harness put on several years ago. Wires now connected properly and soldered.