Newbie w/ some questions.

[Falcons Talon]

Hello all. I'm a newbie in this forum, and although I own a '92 GT and do the repairs on her myself, I don't know jack squat on what to do to improve her performance. I have a few problems with her that are giving me a hard time as well, and I hope that you guys can help me out.

My first problem could be deemed mechanical in nature:
My 'stang really tends to heat up in the city. I have a 160 F. thermostat installed and a fairly new 3 row heavy duty radiator. The fan clutch is fine, and the water flow is good. No visible problems with the water pump either. Is there anything that I am missing that can be causing the car to heat up like this? Could it possibly be a stopped up cat? Would a flex fan help? Would cutting out the cats help? In deep South Texas, the inspections are not hard to pass. They never look uner the hood or chassis to see if everything is legal. I was told that if I cut out the cats, I will need to buy a chip for her.

Problem 2 Quick and easy performance hop ups.
What should I add...quick and easy for starters? I want to keep her as a daily driver, so I don't want to lose much gas mileage. I know I have to sacrifice some for performance, but I don't want her to drop to less than 15 mpg. I have some pulleys on her, but that's about it. I'm looking to get a K&N cone filter, but do I have to buy the complete air inlet assembly, or can I just bolt the cone onto the stock air inlet? Would new headers help? If so, whick kind? I've heard things about shorties, but I wouldn't know which to get. What else is a realatively cheap and econmical bolt on improvement?