I had a '40 1.5 Ton with similar symptoms once. Turned out to be a friggulated, snarffleginked input shaft bearing, the one that is between the FRONT of the MAINSHAFT and the BACK of the INPUT shaft (they overlap, and the bearing is betwixt the twain), causing the thing to spin input & output at 1:1, so of course I was able to drive (forward). Probably the one & only time I was "happy" these suckers are geared so daggone low! Anyway, this was in 1975 or so...Motion Industries I think came to the rescue. Good luck! Not hard to fix, but ya gotta take out the tranny. Know any high school football players? -I could do it when I was 17, not sure at 50!

Stovebolts are like women; as they mellow with age, it's harder to get 'em to turn over on a cold morning, but once they're warmed up, LOOK OUT!