I have a 2001 GMC HD 2500 and I can't get my fuel pump to work. I have changed the relay and checked the fuses (the only ones that I know about). And I also tried changing the fuel pump. If there are any other fuses or relays that I might not know about or a switch somewhere. Please someone let me know.

Welcome to the forum. You have checked all of the components, but did you check for 12.6v power to the fuel pump? Do you have a good ground for the pump? Has the tranny been out of the truck? If the tranny has been out see if they pinched the power wires for the fuel pump in the cross member and frame. Also look at the plug that plugs in to the fuel pump and see if there has been any melting. There have been some problems and you can get repair plugs at a parts store.

I wasn't able to check for the voltage, I have to go get a new multimeter. I did check the plug and it was ok, the tranny has never been out, and there is a good ground. If the pump is not getting the voltage and the fuse and relay are good, where would the problem be?