The mystery hesitating Van

I am driving 2005 Dodge Grand Caravan 3.3 L. Few weeks ago I noticed hesitation when I took my foot off gas to cruise at posted speeds. Sometimes it was very subtle other times it actually jerks you. My engine light has never come on. Took to garage, they changed my spark plugs and wires, cleaned my throttlebody, and dumped some fuel injector cleaner in it. Well 500 dollars later and now it has progressed to my RPMs jumping around sporatically at low speeds under 50 k/hr and still no engine light. Please I need a direction to go on. My husband and myself are going to try the O2 sensor before the catalytic convertor, then move to the TPS ( Throttle Position Sensor). Please help. She has never made a weird noise, or had a engine light pop on yet ( Scared to see what this would have to turn into for it to go on) and she only has 78000 kilometers