It is a lockup yes, just installed a few days ago. Wasn’t aware of the block and tranny age difference until I dropped the tranny and realized the new torque converter and the one for 1976 I ordered were different. Had to have one custom fabricated locally. Was thinking it could be a tranny issue just unsure as to what. The tranny fluid is brand new, as well as the filter and has recently had a band adjustment as well.