2009 Ford Flex Limited 6 Cyl with codes P0717 and U0100

Question

Codes P0717 and U0100 are present has shifting issues, feels like the transmission is slipping

Answer 1

with U0100 and the P0717 its possible the problem is due to a bad ground connection,

there are a few service bulletins from Ford for shifting issues, like hard shifting 1-2 or 5th gear slipping (not sure what your symptoms are)

I would look for chassis grounds, remove them, clean them up with sand paper and retighten them back.