I have 2 busses.
, 1999 with 200k plus miles….50 psi cold idle, 40 when it warms up. 50 psi while driving.
My second bus, 2006 with a fresh inframe, less than 100 miles on it right now.
70 psi @cold idle, drops to 50 psi when warm, does about 60 psi while driving. This one has fresh oil, Rotella 15w40, and new filters and oil pump too.