1992 Ford F-150 5.0 L 4X4 Oil Pressure

Verify preesure when hot witha pressure guage. If the pressure drops then you have engine bearing wear probably both at crank and cam. I have yet to see a bad oil pressure fixed by a new pump. If you are going to replace the pump you should go hi volume to make up for the extra clearance in the bearings from wear. Be forwarned the the stock oil pan will probably not clear the taller oil pump. This can be a costly upgrde. As you noted cold oil does ok. And thicker oil will do the same thing only better.I got away with 15w50 in my f150 when I had a similar problem.I changed the pan the pump and the crank and main bearing along with the rod bearings. I stilll had to run mobil 1 15w50 to get 20 psi at idle hot. And only hit 60 psi going down the road. Still after 5 years when I tore the motor down the crank showed no wear as did all of the bearings. Try a thicker oil first and skip all the mechanical stuff.