My transmission feels like it's slipping and no check engine light comes on

Are you sure your not knocking it into manuel shift? I do that sometimes while driving and then it revs up and I barley notice I knocked the thing over to manuel shift.

Bad sprag gear in transmission I have the same problem with mine (Google it). Happens mostly after down shifting to 1st gear at a light and accelerating again. When it acts up downshift your transmission manually to 1 start driving and then up shift back to 5 when you are moving.