I have a 99 Dodge Dakota that I just put a crate motor in. It runs grear then it suddenly backfires, dies, spits an sputters, sometimes it starts back up, sometimes it won't.

You've spent a lot of money on things without knowing the problem. Why not take it to someone who has a dyno tester? They will find your timing problem immediately. Backfiring is usually due to improper timing, hence, the gas ignites in the exhaust because you have too much overlap or something and too much gas vapor in your exhaust, which is hot and ignites your gas. How has it been timed so far? Did you time it yourself? or someone else? Did you static time it knowing #1 piston was on TDC?