01 grand cherokee 6 cyl running bad

i went shopping yesterday and everything was fine. when i came out of the last store i had to go to i started my jeep and it ran like crap. the little engine light started flashing and the jeep barely would keep running. when i got it to go i would have to shove it in netural at stop lights and had to turn off the over drive to pick up speed on the ride home. my truck ran perfect up to this and is always very well maintained. it was fully tuned last summer and has 101 k's on it now. any suggestions on where to start would be greatly apreacheated.
enjoy the superbowl all!