Cub cadet lt1045 problems

I have a cub cadet lt1045 my motor went bad and after replacing the motor and drive belt my transmission don't seem to want to go. It worked fine before the motor swap and a but a brand new belt on. Any suggestions on what to check next?

https://www.cubcadetpartsnmore.com/cub-cadet-service-manuals

make sure rod at back of tractor is pushed in, check belt routing as well as pulleys & idler pulleys.