Have 96' f150 put an engine from an 01' f150 in in. Changed sensors and all that. Trucks hard to start now.?

Something with the timing. 89% of the time timing is to blame for bad engine starts or no engine starts at all or just crappy engine performance in rebuilt, replaced, or motor swaps. Check and make sure timing is on and that no spark plug wires are crossed. Also check ALL sensors on the engine. make sure the plugs to the sensors are all plugged in and that all vacuum lines are in their proper place. Did you use the ECM (computer) from the truck the motor came from? or did you use the one from the 96? If its the one from the 96 then theres your problem. Make sure all wires and plugs coming from the computer is/are in their right place. These are the main reasons for your symptoms although theres no tellin' what it might actually be.

you say it runs great once you get it started? did you bleed the fuel lines? there might be air in the lines and has trouble for the gas to reach the engine.