Originally Posted by
Visseroth
Here's the 50 cent mod.
https://www.ford-trucks.com/forums/9...-cent-mod.html
Also I believe I recall reading at one time that a bad coolant reservoir cap can cause coolant to overheat because the cap isn't holding back the pressure like it should.
Something worth checking if indeed your thermostat is good and allowing coolant into the radiator.
I have head the same thing about the caps. I guess you don't want the caps that "click" Apparently they were problems in about every Ford vehicle they were used in. They do not allow the system to pressurize which raises the boiling point of your coolant.
As to the power loss I would make sure you are building boost and that your fuel system is in good order, no clogged filters. IF you have a metal tank your intake screen could be clogged up too. (not sure what the 550's ran for tanks. I might be way off base here.)