Trans engages but not @ proper RPM. Diagnostic reads re-programing. Should I just replace trans sensor to fix problem?

Question

Hi I own a 1999 Mitsubishi Mirage 1.5L DE. In these recent days we have had very hot weather. On one of these 100 degree days I noticed the car would run as if hesitating to speed up or engage into proper gear. So I drove to a local shop and had the transmission flushed and had the transmission filter replaced. Drove around town and their was a slight improvement but still had a hesitation to engage into the next gear. So I went to a few other local shop and had the car diagnose. From the read out it stated the transmission is re-mapping or re-programing it's self. We checked for signs of leakage, cracks and the car engages into every gear as the car is parked on with my foot on the breaks. My question is should I just replace the transmission sensor to stop the transmission from remapping or shifting reprogram?