So I've been having temp issues with my 368.  After running for about 20 minutes the temp gauge will climb all the way to high.  I've changed the t-stat and the sending unit.  I've changed the factory gauge with another factory gauge with no change.  I have checked the temps with an IR thermometer and It shows 185 at the t-state housing, 185 at the sending unit, and the rad shows around 150.  I keep thinking it could be the IVR but the fuel gauge works fine and it controls  both.  The motor has been rebuilt. 

Any thoughts or suggestions?