1998 Chevy Tahoe My Tahoe wont start..help!

I was driving the other day when my car started lugging. I was applying the same amount of gas to the peddle but it just started slowing down. I pulled over and within a couple minutes my tahoe shut off. We thought it was the fuel pump since it didnt make a sound when the ignition turned on. So we dropped the tank and disconnected the wire leads. We tested the voltage and it only had about 5 volts on both positive leads. Concluding, it may not be the fuel pump, considering there would be around 12 volts. Is the normal? What could be the reason my tahoe is not starting? We also checked the fuel pump relay in the engine compartment and it still did not start. Any suggestions???
Thanks