I just changed transmission 1 month ago on a 97 sport. Today the car will not go from a stop unless I manually shift it into 1st gear then go into 3rd. When I go into drive it downshifts up hills and goes into overdrive. Any suggestions

 

not sure on the '97, but on earlier models, pull the main TCM connector, and see if it operates correctly under full manual control, if it does, the problem is electronic, such as solenoids, wiring, TCM, sensors, connectors

 

It sounds like you're starting in 4th gear, which would point towards the #1 solenoid in the transmission not working. That would also cause it to skip 2nd gear. Since you replaced the transmission recently, inspect the wiring and connectors to the transmission for damage. If the solenoid is bad, the set of 3 solenoids is around $100 and can be replaced by removing the oil pan and filter.