GM-GMC: 99 c2500 losing all power at highway speeds, stainless steel canisters, tank pumps

Question
vortec 5.7 liter,130000 miles,recently replaced fuel pump. Under heavy acceleration, motor loses power and sounds as if it's backfiring through the intake manifold. also i can hear the fuel pump running loudly while driving(this is during the times the engine is acting up). shutting off ignition for a couple of minutes,then restarting fixes noisy pump, and engine runs almost normally.Please....any idea what's wrong?

Answer
This vehicle is much newer than those I am used to working on, but I will try to help.
I assume that you have an electric in-tank fuel pump.  Your description implies that the replacement of the pump may not have been done correctly.  There is an intake screen on the pump, often referred to as a "sock filter" and this may not have been reattached properly (or a new one was not attached properly).  
It is also possible that the pump itself was not reinstalled correctly.  Most electric in-tank pumps sit inside a baffled reservoir to ensure that they always have a supply of fuel right up to the point where the tank goes dry.  If the pump was not installed correctly, it may starve for fuel and/or entrain air and cause the problems that you are experiencing.
One final thing to check:  The fuel filter.  After disturbing the fuel tank to change the pump, some of the sediment in the tank may have gotten into the fuel system and caused a restriction in the fuel filter.  In new vehicles, these are stainless steel canisters that are usually mounted along the fuel line as it runs from the tank to the engine.  I do not know exactly where it is on your vehicle, but you should find it and change it.