I have a little problem. My car sat for about three months because of the brakes needing serviced. Thats been fixed and i go to drive it around a little. It runs fine until i reach operating temperature and then it seems bogged down alot like two or even three cylinders are not firing properly? It barly breaks 60mph! I drove it like this for about 20 mile hoping maybe theres just some bad fuel in the line or something but it still runs the same. It does have little bursts of running decent for about 3 or 4 seconds. So i took it back home let it sit for an hour and it ran fine again until it got to operating temp. also on a side note it doesnt start running bad like that until its pulling it's own weight "driving around" if it's just sitting there it didnt do it just reving it up?
If anyone knows what could be wrong please help me!!!

spark plugs and air filter maybe a oil change !!