Transmission slips out of gear when first I start car for the day when stopping?

My car just started out of nowhere slipping out of gear when I go to stop and take off again. I checked on it during the middle of the day when it’s warm and the car was running fine but this morning when I went to leave again got less than 1/4 mile away stopped and went to apply the gas and car just revs in neutral basically and the car does not want to grab the transmission back again. This car will not operate correctly if the transmission fluids are at the correct level when cold or hot. It works best when over filled to the hot dip spot when it’s cold since I have gotten the car. I did a transmission fluid and filter replacement about 2 months back and there was no grey sludge or shavings in the fluid when looking. I just replaced the suspension, so I want to kind of pinpoint what I need to replace so I don’t go buying a new transmission for no reason.