I am curious how I can tell if my converter is locking up on the freeway. My freeway mpg has recently decreased to less than my city mpg. I think that I can feel it locking (which I know is not normal) When I get on the freeway, accelerate slowly to 68mph, I feel an "extra shift" or bump at about 50-55mph. ( I really have to concentrate to notice it) I am just wondering if it is not locking and destroying my mpg. The truck runs great on the freeway, just decreased mpg.