1996 zetec 4cyl dohc - 110k miles

Recent work: replaced iac valve, replaced maf sensor, new plugs/wires, new fuel filter, new o2 sensor [before cat.. finally got rid of that damn p0420 code]

First start of the morning the car always gets going just fine and runs nice and smooth. However, once the engine heats up it still runs slightly rough at higher speeds [40mph+] and will have a slight surge at idle. At this point, if I were to turn the car off and back on [say I stopped to get fast food], the engine cranks for like 5-10 seconds before it'll get going again. The more frequently the car is turned on/off, the worse it gets [it also seems to affect the surging].

Also, when driving in the city through stop and go traffic, my temp gauge indicates that my car is running slightly hot [as high as the "m" instead of at "o" where it normally rests].

Lastly, after the car was running rough and exhibiting the symptoms I detailed earlier, I was inspecting the car and noticed that exhaust seems to be leaking out of the front of the cat. I've looked for this a few other times and haven't noticed anything.

Oh, yeah. No CEL codes. I had a p0420 for a while, but as noted above it went away when I replaced the o2 sensor before the cat.

mmm I may be forgetting something but I'm kind of tired.

Any help would be greatly appreciated. Thanks!