"Ok i have a 1966 plymouth Satellite with a 600 hp motor i changed over to a A-833 trans with a 8 3/4 rear with a 489 chunk & 391 gears yes its a posi when i am crusing in forth and hit third hard it hits the rev limiter fast i want more rpm would 3:55 be better or 3:23 any ideas.!"

Try the 3.55 gears. They are a good compromise for some freeway use and should get you up into the 140+ to 160+ mph range, depending on how tall your tires are.

Are you having traction problems too?

Tell us about your 600hp engine combination.