1993 Ford Bronco hesitates and sputters at highway speeds

This is a well maintained Bronco and I recently had the transmission rebuilt, and the motor tuned up. We replaced all of the spark plug wires and plugs, etc. I also had the radiator flushed out and installed a new thermostat.

The engine cranks and runs great, even when it has been sitting for a month or longer. Around town, it runs great, although the temperature sensor seems to run hotter than normal, the engine never over heats. I took it to a radiator shop and they said to put an original thermostat part in it and I did that, but it still seems to run at a higher temperature and occasionally moves over to the over heat area, and it does seem to be running hotter, but the engine doesn't really over heat? Around town it runs great with lots of take off power and it cranks and idles well.

However, when you take it out on the highway, once you get up to around 50-55 miles an hour, it starts sputtering and hesitating. If you accellerate, it will kick out of over drive and take off with lots of power, but as soon as it goes back in OD, it starts sputtering and hesitating again.

I'm not sure if the temperature issue is related to the highway hesitation and sputtering, but I would like to solve both issues even if not.