problem- 03 Avalanche Z71 slipping?

My Avalanche just ped 50,000 miles so I had the trans fluid and filter changed as prescribed. (Deep pan transmission) Now it slips badly at normal operating temps. No check engine light. Engine revs in 1st and eventually catches up then slides and slips into 2nd. At highway speeds it eventually finds overdrive. Slips in reverse as well. It acts like it is starving for fluid but the level is topped off. Any ideas as to the cause? and solution?