Restoring 86 Dodge Ramcharger plow truck

There is No Way in Hell that a worn engine with high mileage should have a "tight" bearing when replaced with "standard." Either you effed up getting the shells in there and or seated, or there was dirt / debri involved, or the shells were somehow damaged.

"Breaking in" new bearings is not going to raise low oil pressure.

Hard to say, at this point, what you may have done.