If its gutless and sputtering while running hot i would check to see if you have a ballast resistor on the fuel pump. I ran into a simular issue on the XJ. Temp comes up, truck runs like crap, temp wont come down. The ballast resistor takes your 12V system to 9V to make your pump quiet which was a complaint in the past,.. when they crack the voltage drop which give low pressure forcing a lean scenario. Lean equals Hot! The hotter the engine bay the worse it gets,.. just an idea from my past,..