Hard Shift from 1st to 2nd

My point is that if it's shifting from first to second, it's under power and off the idle circuit and idle stop- that leaves the kickdown linkage as the only thing that could have changed before and after the R&R. Make sure it got reassembled correctly and adjusted properly.
And for what it's worth, make sure the fluid level in the trans is good- checked warm and in neutral (not Park) while running.