Did you check the transmission fluid? Do you know how to check it? Get the car up to temp, and run it through all gears [R, N, OD, D, 2, 1] while leaving it in each position for several seconds. Repeat that a few times, and check the Transmission dipstick.
It'* highly unlikely that you are low on fluid, and getting those symptoms, however the fluid can tell quite a bit about the transmission'* condition. Be sure to note the colour and odour of the fluid [don't be afraid to smell it]. Just don't taste it, not a good comparison, all tastes the same