1999 Expy AWD Vibration on medium/hard acceleration

[jcrisman]

I started to notice vibration coming from the front of my expy between 30-40 mph or when the engine is under load going up medium inclines. The harder I accelerate the more pronounced the vibration feels. When i accelerate slowly I don't feel anything. Once i get up to speed on the highway it runs perfectly normal and smooth. I have been reading alot of posts on the internet ranging from front drive shaft to the Torque converter to a bad coil on plug. Where should I start looking? Your help is greatly appreciated....