I was on the hwy today doing about 50-60 mph when the transmission seemed to have slipped out of gear. Looking at the gauge cluster I saw that both the D and L lights were lit at the same time. However there was no apparent downshift/revving/ or engine braking that you would expect from suddenly downshifting at that speed. Not knowing what to do I shifted into neutral and then back into drive and that fixed things until I got off onto a side road where it happened again, and then again, before I got home just a mile or two later. What could be causing this, and what is even happening? It makes no sense to me.