Tranny Problem

My 04 runs great but when I stop suddenly and attempt to drive off the transmission slips. The oils is nice and clear, level good. Could this be some sensor problem (I hope), filter or the worse-tranny going bad? Only has 57K miles on it. Once I sense the trasmisson engaged it drives great. No slipping once it's up & running. Some mechanics informed me there might be a vauum line at the back of the tranny that might be loose. Any suggestions are greatly appreciated, thanks.