Welcome to the Forum.
I agree, having a history & current code scan may point to the problem area.
A more advanced scanner is required, I had mine initially read by a Snap On scanner.
4t65E can develop shifting irregularities, and we will know more once the codes are read.
Please back the code results and can you tell us if the transmission fluid & filter was serviced recently?
Is your trans dipstick fluid on the full line after it'* hot/driving for 20 minutes?