1990 hatch with a 1.5 sohc and a 4 speed auto, once up around 60mph+ the car feels like the trans just slips a tiny bit then grabs, almost like its going out of "overdrive" into 3rd and then back again. It shifts fine otherwise, holds speed, downshifts fine, fluid is clean and does not smell burnt. Cause for concern?

 

have you looked into seeing if this vehicle had a filter on the transmission?

 

Im sure it does, at least a filter shows up as available on advanceauto.com i was thinking of putting in a new filter, shift solenoid, fluid etc because its all cheap stuff to check off the list.