1991 Toyota Previa Previa hesitates, or hiccups

The check engine light just came on, the change oil light has been on for a couple weeks while we have been replacing parts and trying to figure out what could be wrong. The Previa will hesitate kind of like a hiccup, it doesn't loose any power when it does this and it will happen in a higher rpm while foot is on gas petal. I have replaced the fuel filter, the throttle position sensor, airfilter, distributor cap, rotor, spark plugs and wires, haven't changed the oil but was changed not too long ago and still has the honey color to it. More recently within the last couple days of driving the Previa it has started to stall out when decelerating and coming to a stop, and the idle will fluctuate, and this is when the check engine light has come on. Any ideas of what is wrong or what I could look into next?