I'm working on a 98 Caravan with a 3.8. Driving it with a scan tool hooked to it, the ignition timing is going nuts under moderate to heavy loads. The timing is momentarily dropping down to 7-14 degrees. It will do this from off idle to 5K. If you let off the throttle it goes back to 30+ degrees. It's giving no codes. Numbers from the Map, TPS, O2, and knock sensors look normal. What do you guys think?

Thanks,
Kevin