91 trooper v6 sohc

my problem is this my trooper has 170000 it ran great and now all of the sudden it has a sever hesatation bucking and lack of power i did a complete tune up plugs wires coil fuel air and oil filters and still no change the odd thing is the check engin light is not on however when it does come on the thing smoths right out i have no clue what to do help me plz