My transmission does not shift into 6th gear for quite some time when the engine is cold and outside temperature is 25 degrees or less. Letting up on the throttle does not seem to help. Does the engine need to be a certain temp before shifting into high gear. I live about 1 mile from the interstate and don't like the high rpms to maintain speed. Any info? Still under warranty. Just haven't had time to take it in yet. Thanks.