New Guy, 72 Plymouth Duster, where to start looking?

Oh, one thing to add is my oil pressure on a fairly freshly rebuilt 340 engine is 50-60 psi parked running and then 40 psi running down the road most times and if engine is pulled down by transmission when on the brakes after warmed up on a hot day and running 3800 rpm on the highway, 20 psi briefly. In that instance I shift to neutral and get back my 40 psi.