My guess would be that the gear lube in the tranny warms up and thins out. The gears can spin easier in the thinner lube. At least thats what I tell myself when my '54 does the same thing. And I rebuilt the tranny 4 years ago.

Chip

And yes, I did take my comedian pills. Do I need to modify the dose? wink

Preaching the Hot Rod Gospel according to the 4-stroke apostles:

Suck, Squish, Fire and Fumes