Transmission shifting hard when cold and warm

You did not mention which engine your Magnum has. Your transmission fluid should be changed every 60,000 miles for "severe duty" -- which I would use as a benchmark. Has the fluid been serviced in the past? You could have an internal mechanical concern, but it's really hard to know without hands on testing with diagnostic equipment attached. Seek the assistance of a local shop near you -- https://repairpal.com/repair-shops/dodge-repair-and-service-in-st-louis-missouri