Transmission replacement 71 Cheyenne

[Orion 762]

I've got a 1971 C10/Cheyenne with (I think) the original TH350 Turbo Hydramatic tx. 2nd gear has started slipping, and I need help sorting out "what's next".

A local tx. shop (with good reputation) can "rebuild" the old tx. for about $550 (quoted). Is this price in the ballpark of what's expected on these tx's??

My local Chevy dealer quoted a DELCO factory rebuilt for $1,300 (with 24K mile warranty).

Any experience on "which to pick" (cheapo rebuild vs. DELCO), and are there other transmissions out there that might work better at reasonable cost? This truck has the "pulling package" rear end (lower gearing ratio). (My son said the rear has 411 teeth instead of the normal 308, but not sure what this means. I do know that at 70 mph, the engine cruises above 3,000 rpm, and this high RPM is related to the rear end design.)

Just posting here for "suggestions and hints".

Thanks . . . Orion 762