I have a 01 dodge 1500 that overheats when driving in fifth gear and 60 plus mph. I can slow down and it will cool down. I have changed the fan clutch, thermostat, and radiator cap. The coolant is not dirty at all. I just bought pickup and wondering if it has been hot and has blown head gasket. It runs fine. Any help would be appreciated.

Don't rule out the possibility that you need to replace the radiator. Mineral buildup, from not using distilled water, can cause overheating--requiring the radiator be rodded or replaced. I would replace it.

If you have a blown head gasket, you would likely know it--possible loss of power, coolant, and oil. Running a compression check on each cylinder will help you resolve that issue, if your fluid levels appear okay.