Lately, my car seems to shift at a higher RPM when it first moves after being still for more than a few hours. For example, it shifts at 1800-2000 RPM instad of the usual 1500 RPM. After the car is in motion for a few minutes, the shifting sequence reverts to the more normal RPM range. Is there something that needs to be checked because of this behavior? I changed the transmission filter and oil a few months ago and did not notice any problem when I changed it. The car has 90,000 miles on it. Thanks for you thoughts.