Got a problem with my auto tranny. It won't shift out of 2nd until it's well warmed up. After it shifts the first time, it works fine and won't do it again unless the car sits for several hours. The problem has been getting worse lately. Checked the shift solenoids, they were ok. Changed the fluid, it looked fine, nothing dark or burnt. The car only has 100k on it. Any ideas what this might be???