I doubt it`s a gear issue ....sounds tune related/engine related.
Those gears are a good match for a 700r4 and that combo was installed behind many 305 smallblocks.
Sounds like you need to do some engine testing ,check the valves,compression test,leakdown test,sounds rpm related ,such as bad advance on distributor,clogged exaust,bad cam.....check for blowby also.

I really doubt its gear related.