I have a question. My dad has an 83 f150 inline 6 with a c6 trans. And my uncle has an 82 f250 460 bigblock with c6 trans. But his truck revs really high . For example you are hitting 2,100 rpm or so at 45mph and you try to pass a car and accelerate. The motor revs high and struggles to gain speed. Im thinking that the c6 is too small for that bigblock. Or is it normal since trucks werent really focused on fuel mileage back then?

 

Assuming your uncle's C6 is okay, his truck is probably just geared (axle gearing) low for heavy towing. I-6 trucks like your Dad's, seem to have been often geared higher for economy.

Original C6 transmissions were designed for big block engines; small block C6's followed later (same basic internals, with a different case/bell housing).

 

460 not available in 1980/82 F250/350, only available in E250/350. So it's either a 1983 or it has a 400. 460 reintroduced in 1983 F250/250.

 

Its adapted