Transmission trouble
 

My 06 Buick Lacrosse with 135,000 miles on it has an intermittent transmission problem. When it is at operating temperature while cruising on a level surface, sometimes it will shift up or down one gear. The auto repair shop never saw this happen while driving it today. They quoted me a price of $340 to change the fluid and install a new filter. Because my car is so old can I just ignore this minor glitch and drive on? I am not able to work on the transmission myself.

Might be a good idea to get a few estimates,sounds a little high.