maybe a OEM exhaust again, and heat shields
do you run syn oil?
as if not, it could help a LITTLE on heat, or I sure noticed a difference when I switched, as my fan doesn;t come doing same things it used to on Dino oils!
which also makes me wonder, does your fan come on often? or at all?
could be you have a bad temp switch or fan control unit if not
and remember heat can damage more than plastics, as if your heat shut down switch isn;t working or fan and tempo switch, you can over heat your motor and ruin it it?
NOT saying this is happening, just food for thought!
and again if your having running issue's, maybe compression is off or on its way down?
I have a 400 foreman the smaller brother to your 450, and its never ever had any issue's with running in any temp, and have owned it since new 20+ yrs ago, and its run in minus 30 to 100+ degree temps, working it too, not just joy riding!
idles just fine ion all temps, and just runs the same!