We're losing power driving over 35 mph. Check engine light keeps flashing low temperature coolant. This is whacking out my throttle position sensor.

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I have changed the temperature sensor and at the throttle position sensor. I have also replaced the thermostat with another 195° thermostat. I recently have changed the spark plugs and the distributor cap and condenser plus new wires. I have checked the hoses with starting fluid to check for leaks and have found none. Today I replace the clutch fan because the other one was stuck and not spinning freely. I thought this was the answer to my problems. But the engine keeps running cool and the engine cuts out on me if I try to go to more than 30 mph.I do have and exhaust leak on the right side manifold but I do not think it is that bad. I have also replaced the radiator cap and am running fullscreen antifreeze in the radiator. I also replaced the coil. This problem actually started about 10 months ago. I thought I was having a fuel pump and filter problem so we had that replaced at that time. Please help I am running out of solutions. Thank you so much. Mark & Cathy.