EEVEE

So i made a post about this a while ago on how my revs hang when tapping my gas pedal. But i should explain more issues to maybe see if itll connect to something. Anyways details 1999 with 204k miles and all stock.... meaning theres not much new parts besides a fuel pump, track bar and other idds and ends i kinda forgot. Anyways yes on random days my jeep turns back to normal with its revs i tap the pedal and goes back down like normal yay. But then some days like today they hang how i know this another way is if i keep the shifter in the 1st gear when its normal right when i let off the pedal itll engine brake but when its acting up itll still go for a second or 2 then engine brake. So it would help if i get some suggestions. Another thing i noticed when i had my check engine light on for the evap purge valve or solenoid thinga majig, When i first start up after it is warm and go to take off it loses alot of power and sputters but if i give the gas pedal a stab it takes off and poof everything back to normal. After the light mysteriously turned off it still faintly does it. Is that just gas fumes built up in the system making it run very rich? Ok so thats all the info i really have i can give a test to suggestions to narrow this down. But im gonna tune it up tomorrow and maybe show pics of what the spark plugs look like. I feel this is either a sensor issue, fuel and emissions and or maybe the catalytic converter? It is still original but i plan on changing the entire exhaust system down the road but maybe the cat is getting clogged? I should get my hands on an ir thermometer and measure the temps before and after the cat. oh and a little other info as i mentioned some days it has a good kick of power and pickup and other days it feels a little doggy and sluggish. Also how do i properly reset the computer and everything to relearn? After the tuneup i want to reset everything.