trans issues

Shifting from 1st to 2nd at 6500 it doesn't shift until 7500 very harsh. Checked shift linkage, fresh rebuild.Possible valve body ? it is a reverse manual

Is the valvebody a low band apply unit in 1st? What brand, model? If so, sounds like a 1-2 problem with the low/rev band release - kickdown band apply. If not, the only component that applies during the 1-2 is the kickdown band. Not too many things to check.