Arizona Heat Problem 6.5TD
 

Hello everybody i recently just bought me a 1997 Chevy K2500 6.5td F engine the problem is it seems to run a little hot out here in arizona due to the 115 degrees outside. I ran this truck in Wisconsin were i purchased it and never jumped over 1/4 of tempature but its alot cooler down there, My truck now runs between 2/4 and 3/4 of tempature and seems to lack on power when hotter im running 15w40 now in summer just did thermostats and flush no change should i run a heavier oil due to the heat outside put some kinda additives or any ideas???

Help anyone !!!