oil pressure problems

Recently rebuilt dodge 318. Professionally installed cam bearings, turned crank, cleaned block, and checked bottom end after assembly. Rest of the work I did myself. Initial start-up 80psi oil pressure. On its first outting (18 highway miles) oil pressure was above 60psi until I stopped at an idle it dropped to zero. shut it off went to work. After work started it, oil pressure back up to 60psi. 8 highway miles later the pressure was way down at highway speeds, shut it off waited 30 minutes pressure back up to 60 but only couple of miles. End of the affair oil pressure wouldn't get above 20psi and underside of hood and engine compartment sprayed with oil around right front corner of engine?? Are the problems related? any ideas whats gone wrong? Oil pump is new mechanical guage is new oil is 10-30 and new at start of episode.

First thing you do is to make sure you have enough oil in it, then while at home just start it and look at the engine while at an idle and see if your intake gaskets are sealed good, if so check and make sure your head gaskets are seated good, by checking around the right front( I think that where you said) you should see oil seeping or spraying out. If you don,t see anything look for other oil leaks. The last thing possible is that the oil pump is defective.