Shifting problem

I have a 1989 Brougham that I inherited a couple of years ago. It has a weird shifting problem. After a few miles at freeway speeds and then when coming to a stop, it seems it won't downshift It almost kills the engine and then releases. Then when accelerating away from the stop, it seems to upshift rapidly and even causes the engine to bog down and knock. I used the shift selector to downshift and it makes no difference unless I shift all the way to '1'. I suspect it's the torque converter staying locked up. It doesn't do this while at lower speeds around town, only after a few miles on the freeway. After 2 or 3 of these problem stops and starts, it acts fine again.
I'm thinking it is temperature related but I thought that the freeway driving would be easy on the transmission and not cause it to heat up and the constant shifting in town would cause more problems.
Any ideas?