I have a 2007 Chevy Uplander LS. Sometimes when starting from a complete stop I get a loud clunking sound and almost a lurch before the vechile begins to accelerate. This normally happens if you accerlerate fast off the stop. If you go slow and steady this issue does not seem to occur. The best way to describe it would be to having loose gravel under you tires and them spining to get traction before taking off.

Ideas??

 

How many miles on van? Are you the original owner? Is the transmission fluid up to the full line?