Please help?!?! (Car Question) Starts ok cold but rough start when warm...?

Ok here are all the details to this thing going on with my car. First so everyone knows, it is a Chevy Lumina z34 1993 with a dual cam overhead v6 in it, 3.4L. Ok now second we have replaced the air filter, air breather, fuel filter, and have checked all the fuel lines, poured fuel injector cleaner in the car and cleaned battery wires, changed the spark plugs and changed valve cover gasket (different problem, there was oil on the spark plugs for a while so ya hehe). The problem with my car is that it starts decent in the morning when i have let it sit overnight, and also starts good if you start it up right after you shut it off, but if you let it sit for like 2 hours or so then you have to give it gas to help it start (feather the pedal). So everyone knows also, the temperature gauge (inside the car) slowly gets over half (has gotten really hot, up to 260 degrees actually, and i thought it was the thermostat but i don't think this will affect how the car starts will it?) Anyways, then drops back down to a quarter, then slowly rises again and repeats, it doesn't seem normal but idk. Another thing is i filled the car with gas (completely full) and the gas tank leaked about half a gallon of gas and then stopped. (The leak came from underneath the car in the middle, where the gas tank is). Any ideas on what is wrong with it yet? Anybody? If you have anymore questions about info of what I have done with the car, noises it makes or anything like that, just type it up here on the page and I will answer back within a couple hours. TY, please everyone help! So in need of help!!!!!!!!!!!!!!!!!!!!!!!