2000 Nissan Quest engine running really rough!

Alright, the car use to drive good when it was cold and then started jerking like if it giving out, then as time went on it started getting worse, it would start turning off as soon as you give it gas, if it didnt turn off it would just be running rough like a kid trying to learn stick shift with a heavy duty pressure plate, thats exactly wat it looked like and felt like, well whenever it turns off, it cranks right over no problem, like if theres nothng wrong, so that cancels out the distributor in my head, we changed spark plugs wires, fuel filter we checked fuel pressure, constant 35psi, the cat and manifold are getting cherry red so I thought clogged cat, so I disconnected the pipe and ran it straight pipe, still same thing so cancels out that, now im stuck, no check engine light, only knock sensor like every other nissan quest, so yea if anyone can help we would really appreciate it.