Truck slows down after driving a few minutes

My gas gauge stop working and the mechanic said that I have to replace the fuel pump to make it work. Also, after running for a few minutes running over sixty five the truck starts slowing down like it is not getting enough gas and I have to stop and turn it off to make it work again. What it can be? I took it to the Autozone and was told that it was a fuel injector and then I took it to an other place and was told that the injector was not the problem, they said that the problem is my gas pump since my gauge is not working that is what is causing the problem. Can it be that or there is something else? Little help will help me a lot.