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!!!!!!!!!!!!!!!!!!!!!!!Please help?!?! (Car Question) Starts ok cold but rough start when warm...?
Well to start your seals are leaking. That is how oil got on your spark plugs. If oil is leaking then you probably have low oil. That can be very bad. You must check your oil every time you get gas. You have been lucky up to this point. If you run the oil reservoir too low you will seize the engine, it will freeze and will not work. You either get a new engine or new car. It is worth the two minutes to check the oil.

Second it sounds like your water or antifreeze is low too. I know everybody is in a hurry these days but you need to take care of the vehicle that takes care of you and keeps you protected.

Terrible things can happen to you from sheer laziness.

Picture breaking down in the wrong part of town all alone in the dark. You will wish you took the time.

Start caring better for your car it will run for more years to come.Please help?!?! (Car Question) Starts ok cold but rough start when warm...?
you say it,s hard to start after it warms up? this is just a guess but have the coil tested. if a coil gets too hot then it can break down and hard to start. you say the tank leaks? maybe it,s sucking air from the leak.Please help?!?! (Car Question) Starts ok cold but rough start when warm...?
if a car gets too hot it is harder to start until it cools alittle bit then should start fine. you do need to find out where the gas leak is and repair it im sure its not helping the situation at all.