I adjusted my TV cable and that fixed my problem... for a while. Now the truck is back to shifting to second around 35 and third at 55 and hasn't shifted to fourth yet (even after 85mph.) When I slow to a stop it won't downshift to first unless I wait about 20 seconds, otherwise it will stay in second gear. The fluid level and color are both fine and this trans is a GM rebuilt, was dealer installed in '99, and has about 60k on it. Could the TV cable be slipping and losing its adjustment causing this? What are some other things that would cause this?