New Engine Won't Run

My dad decided to replace the original engine in his '93 pick-up with a rebuilt one. Both are 22RE engines. This project has been going on since January, and yesterday was the first time we tried to start it. As far as we can tell, everything is hooked up correctly. The problem is, the engine will start, run for anywhere between 5 and 15 seconds, then quit. It sounds fine until it stops. We've double checked the routing of the vacuum hoses against the diagram on the hood, and everything matches. The spark plug wires are also connected correctly, it hasn't run long enough to adjust timing. It seems like its either not getting enough gas (though the fuel system seems fine as far as we can tell... it does start after all), or it is shutting itself down for some reason. We checked for engine codes by putting a jumper between the two data ports specified in the Haynes manual and checking the engine light. There is oil pressure, the oil light goes off when it starts, and the check engine light goes off when it starts.
Anyone have any ideas? I can post pictures if it will help, just let me know what you would like to seee.

Thanks for the help, I appreciate it.

Check the Tube between the MAF and the Throttle body for any leakage, cracks or holes. Make sure all of the connectors are tight!! Any air leak between the two will cause this problem. Also make sure the MAF is working!!

Check the Tube between the MAF and the Throttle body for any leakage, cracks or holes. Make sure all of the connectors are tight!! Any air leak between the two will cause this problem. Also make sure the MAF is working!!

I passed the info on to my dad and he finally had a chance to check that out. He said it seems to be fine, no leaks, everything is tight.... and it still won't run. I do appreciate the reply though. Any other suggestions?

Thanks

throw a fuel pressure guage on there, engine may be completley fine but the fuel pump may over heat. im doing the same to my 3v-ze egine and had the same problem