Hi,
A friend of mine bought a new 65, had 3.73 gears, blew them up sometime in 67/68 as he traded it in on 68 Z28
Tony, you don't say your tire size, but I am running a 3.55 with 245 60 r14 and it runs 3000 @60, 3500 @ 70, 4000 @ 80, sounds like what you might have going on.
One funny thing Pontiac had a 4.33 vs Buick had a 4.30, why?
Also the Pontiac had the stronger 8.2 casting as Oldsmobile would use Pontiac axles for anything over 3.08, 3.08 could have either Buick or Pontiac casting, in the 442's.
Regards,
Jim