transmission slams into gear when warm.

It seems as though no one has this answered. And I don't either, sorry. I have the same problem now w/ my 2007 Buick Rendezvous w/ 125,000 miles on it. I just had the transmission fluid & filter changed and it still happens occasionally. Everything seemed to go awry when I had a damaged left headlight replaced from accident. I get the no seat belt usage gong one time every 7/10ths of a mile plus then the gong sounds again for every left turn signal pulse until I use the right turn signal which extinguishes it until the 7/10ths bit starts it again. It's just aggravating from such a fine automobile(CXL). My only conclusion which "I" believe it may be is the computer. At times I mistakenly blame others. Did the dealer change out the computer because another vehicle has the gong problem? I'm frustrated as you are. Hopefully you and others can view this response. I hate buying new cars. 0730hrs 22mar2015