The dead fish smell could be the cat just getting VERY hot. Mine does this all the time if I romp on it, esp. flooring it up a hill or something that puts the engine under heavy load. (Big boost with a stock cat doesn't work so well...)
Something like this sounds likely in your case, esp. with your CLT temps being through the roof.
Make sure there are no leaks in the system and you have enough coolant. If that's good, then my guess is your thermostat is jammed shut. Good test for this? Feel the upper rad hose when the engine is warm/hot. If the hose is cold, your 'stat is shut and needs to be replaced. For that matter, if you just got this car, replace it anyways...they're like $20 IIRC and when something like your engine's life is on the line, it's best to just do it.
Looks like others beat me to it while I was writing this post.