Before they open the trans to replace the pressure reg assembly.... they should do a pressure test to see if the pressure is within spec.
They should take readings at idle and stall (WOT) in Dr and Rev
D pressure should be 83-103 psi at idle and 120-170 at stall.
R pressure should be 140 psi at idle and 220 psi at stall.
Stall and idle readings will be dependant on how throttle ("kickdown") linkage is (mis)-adjusted.
Edit; I'm gone for a week... probably no computer access for a while....
Silly off topic story.... I'm driving an old school bus to Whitehorse, Yukon Territory, from Edmonton, Alberta... approx 2000km trip.
My brother lives in Whitehorse and he's like the last hippy or something.... he sent me money to buy this 1991 International 36 passenger school bus that he will convert to a "motorhome" that he's gonna live in, after I get it there... He's also sent money for the trip and paying for my flight back.
Coulda put it on a low-boy and trucked it up there for less money.... but where's the fun in that...
It's 6:30am here and I'm leaving right away.... see you in a week!
(I shoulda had the bus painted like the Partridge Family ... oh well, too late now....)