Ok uncle!!! I have a 95 4.9 straight 6. I have replace the radiator and water pump (less than a year ago). Just replaced the thermostat and that seemed to have solved the problem. I ran it to work (17 miles) and it started running hot again (gauge running on A usually rock solid between O and R). I added more fluid because I may have had an air pocket. That again seemed to fix the problem until the next morning. Did the same thing! I have had to add fluid every morning and afternoon for the past 6 days. Not alot of fluid but (less than a quart) still having to add it. There is no sign of leaks from hoses, water pump, thermostat.... Nothing. So if any one has a suggestion feel free.

 

Might help if you post in the right section