Have your original radiator boiled out / repaired.
Flush your system. I'll guarantee the bottom rear driver side corner of the block is sludged up. Remove the petcock fitting and poke around in there. Use high pressure water, etc.
Are you using a zero pressure radiator cap?
I use a 4psi cap and a 160T stat. The truck pretty much stays at 180 on the highway and at idle.
