My TCM will not function as required. Continues switching at the selector.

Hello, are you saying the gear selector shows that it's not in drive anymore when the problem occurs? I'm sorry to say that testing with a suitable diagnostic tool capable of evaluating the transmission electronic controls and shift mechanism is what is needed to find out what's going on here. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops