2004 9-3. Trans slips over 15-20 mph in auto mode and over 2nd gear in manual mode

2004 9-3. Had the gearbox malfunction warning, but after running it through the grears on the manual side, the warning light went out. Never had limited performance. I brought it into my mechanic. No codes no code history. I had them do a trans fluid flush and replace. Now it won't go over 15 mph as an automatic or above 2nd gear as a manual. Suggestions? Now I have no warning light about any malfunction. Did my mechanic fail to properly reconnect the sensors and/or something else when doing the trans flush and fill?