why won't my truck keep running?

what would cause the computer to not communicate with the scanner?

As previously mentioned, possibly a simple blown fuse. May need a circuit diagram or google DLC pin tests for OBDII vehicle. Again I ask , how did you arrive at 60psi fuel pressure?

used a fuel pressure gauge at fuel rail to get 60 lbs. pressure. check all fuses inside and under hood.

Start by maybe getting access to the DLC and harness to look for loose/pushed back/damaged pins in it. Then inspect harness wires for obvious physical damage. Next step would be pin tests for the harness to confirm continuity to the PCM. Actual wiring diagram would be very helpful.