what is making my transmission slip back into a lower gear after i get up to 45 on 2007 Dodge Ram 1500

when the transmission changes to higher gear and i'm above 2 rpm it slips back to lower gear and now the malfunction light is on.

Asked by for the 2007 Dodge Ram 1500
You need to have the PCM(computer) scanned to retrieve trouble codes. Could be a TPS(throttle position sensor) or other things. Won't know where to start without a trouble code.
do i need to go to auto parts store or dodge dealership
The parts house will not be able to retrieve trans codes. You do not necessarily have to take it to the dealer. A qualified independant repair shop can diaginose this problem.
I would seek out a trans shop. You must know someone that has a recommendation for a trans shop.