I might have the solution for you buddy.
When you run your fuel tank low, past a qtr full, the fuel pump itself isnt fully submerged in the fuel, and the lil pipe that runs to the bottom of the tank can come loose, and crack and what not. This cause the fuel supply to not happen at its full rate.
The fuel pump can also get warm, and burn out, the fuel helps to keep it clean.
My car is currently doing the same thing, and i will have the pump replaced shortly, will cost me nothing, hello warranty :D... or by taking you fuel pump out, and fixing the pipe up properly will maybe fix this problem.
This tho is a stab in the dark, i know its the problem in my car currently, and has same symptoms... but you never know engines, they always play silly buggers on ya :(
do you find if you punch it, left off for a sec, and punch it again, it will rev hard all the way to 5grand? if so then yep, new fuel pump for you :(