Our 1964 Lincoln Continental is shifting up/down at slower than highway speeds on our trip from LA to SF. Transmission is overheating. Any recommendations? I left LA on Friday and about 5 hrs in, after driving at about 65-70 mph, we got stuck behind a slower vehicle and ended up doing about 45 mph. That's when the shifting problem started. We stopped for about 20 min before getting on the freeway and it was fine until we got near our destination and exited the freeway. Now we're heading home and only 1 hr into drive and the problem has started again (we're in slower traffic). We were planning to take a few breaks anyways, but I want to get home some day!