94 Chevy/Geo Tracker manifold glowing

I have a 1994 geo tracker, 1.6 litre automatic, it has 183,000 kilometers on it. I havent had many problems with it, just minor things. I've replaced the valve cover gasket and changed the oil just last week and I noticed the manifold glows orange after I drive it. I can smell it getting hot and it has started making my valve cover gasket leak again, so i'm afraid it may start a fire. I thought at first it must have been a clogged catalytic convertor, so I removed it completely. It still did it, so I replaced the whole exhaust system, from the downpipe to the tailpipe, I put on 2 1/4" exhaust from the downpipe to a cherry bomb exhaust. The exhaust is flowing fine, and i've gained some power back(it had been losing power), but it still isnt back to its full potential, and it is still glowing red hot after 10-15 minutes of driving.

i removed my air intake and left just the throttle body seeing if maybe it wasnt allowing enough air in, but it hasnt helped. I'm stumped from here. I changed the fuel filter, I know it must be running too lean to do this, but what can I do to fix it? Have you seen this problem before?