My 4.0 starts great when cold, but is very hard to start when hot. Any ideas?

Sounds like the electronic module needs to be replaced. Unplug the old one take out the mounting screws get a new one at the auto parts place plug it in replace the mounting screws and it should be ready to go it's not hard

I don't know if you are talking about outside temperature or engine temperature. If engine temperature-it could be the ignition coil or coilpak or fuel pump. If outside air temp- then the cold start circuit acts like a choke and the engine is too lean to start good when the cold start circuit does not work in hot weather. There is a temperature sensor in the air bonnet for incoming air.