My 94 diesel with I guess is a 46RH locks up at ~45 MPH. It's annoying, because that's the limit here on the highway, and it will hunt unlees it's on cruise. OD is higher, around 55- 60.
BTW, it won't start right now
https://board.moparts.org/ubbthreads/show...e=0#Post5848874

I haven't got the 1940 running yet, it has a 518.
The factory manual might have that info, but I don't have one here.