what is wrong with my fuel gauge in my truck it works some times and sometimes it dont

sometimes my gas guage shows a fuel level and sometimes it don't, but it is never accurate and shows empty when full......tried unplugging the neg bat cable to reset the CPU, but it didnt work...

Fuel sender is probably bad. Sender & fuel pump is one assembly and located in the tank. You will most likely need to replace it.

It could also be the cluster.. how many miles on your truck?

had the problem since i had the truck with 90k. 111,000 on 'er now.

I would have the cluster checked before you start replacing the fuel pump to find out that is not the problem.