Please help me help my cousin. Her 02 dodge 5.9 liter is avg. 11.5 and she cant afford to fill it up or to sell it. i have been helping her as much as poss. It has 126,000 mi. on it and it idles odd with a recent service (IE plugs wires etc.) and her engine light is on. the tires are new. any upgrades that would help would be great. I can get them for her. would filters or anything else help.

Sounds like still has some tune-up type needs. May need to eb put on a diagnosois computer to find out why it's idling rough and engine light is on. Any easy thing to try is to run a couple cans of fuel injector cleaner throug the gas tank if she has not used this type product in awhile. The problem may be worse than dirty injectors but wouldn't hurt to try for < $2 a bottle.

could o2 sensors be the prob?

One more thing I found out when i had her truck her a/c will work when moving but when stopped blows hot?

Pull trouble codes and fix the engine. Then you need R134A in the A/C system.