Engine runs great, after it warms up it tries to cut off.

What is your question?

Its a 92 dodge d-150 with a brand new 5.2 magnum. It runs perfect, and then after a while it cuts off. Thought it was the fuel filter or fuel pump due to the fact that we let it sit for two months while the engine was being rebuilt and installed. Already replaced fuel filter, and fuel pump relay. Before I go any further and replace the fuel pump I wanted to see if anyone had any ideas of what else this could be. Also for some reason the ac quit working (even the fan), but when I tried turning the ac on, then switch it off, the truck idles very low, and seems like it wants to cut off again. These issues could be a combination of different things, please let me know if you have any suggestions or ideas, Thanks!