1988 26’ Navistar Truck

Truck runs and drives well. I just drove it 2,500 miles fully loaded cross country without issue. New tires and rear air bags. Upgraded stereo. Just had oil change. Myself or my neighbor owned this for last 7 years and it's been well taken care of.
It has a few things that need some attention: oil pressure sensor is jumpy, probably has exhaust leak (I drive with windows open), air conditioning unhooked, 4th gear will jump out when under heavy load (just hold it) and the door lock doesn't unlock from outside.