1991 Dakota 2.5 will not stay running

My hubby has a 1991 Dakota with a 2.5 engine. He recently replaced the engine, and now it will not run. It will crank and run for maybe 5 to 10 seconds, then it dies. If you restart it, it will do the same thing. He has tried 3 fuel pumps, replaced the throttle body and the distributor. He took the gas line loose from the throttle body, and it is getting gas. But it acts just like it is running out of fuel. Thanks in advance!!