Look for the loose/leaking vacuum line or fitting, probably bumped, loosened or broken as you worked on the engine.

Follow the vacuum line from the brake booster source line ahead of the check valve, to the proportioning valve on the injection pump, back to the blue vacuum amplifier on the driver's side fender, through the switchover valve and finally down to the transmission vacuum modulator.

Low/no vacuum = higher shift pressure = harder shifts.

Best Regards,
Jim