Take it back to them and have them either do it right or refer you to someone who can. I assume that they serviced it by doing the internal adjustments and changing the fluid and filters. Sounds like they either didn't get the valving cleaned out before they closed it up or there was a problem that the new fluid masked for a short time. (A reputable shop would have tested the tranny first to see if it had problems before doing a "service".)
