1997 Lumina Hard to Shift when temps are cold.

Question is on a 1997 Chevy Lumina 3.1 liter engine 103,700 miles, no leaks or noises, automatic transmission, recent service October 2006 the radiator was flushed and filled, new spark plugs, and the automatic transmission fluid and filter were changed. When the outdoor temps are less than 70 the transmission shifter is hard to move but during the summer months it works fine. In winter I could barely move from park to reverse and on to drive.