I used a TH400 in my '63 C10 for years. Never had any problems with it. I swapped it in because I kept blowing the clutch bands in the old PowerGlide. It had problems keeping up with the 325 horse 400sbc I had in there.

Dave

1963 C10 Longbed Fleetside (1977-1987)
1962 C10 Shortbed Stepside (2003 - present)
2006 2500 Dodge Quadcab 4x4 (2007 - present)