intermittent accelleration

I own a 2001 Chev. Venture with 85K. I recently noticed that it hesitates when I apply the gas pedal from a standing stop. It doesn't do it all the time. Also, during accelleration, it "jerks" or "bucks" when it changes gear. Any Ideas???

my 2000 did that once with the jumping of the gears, and still does the gas pedel thing

have your vehicular diagnostic tested by someone with an obd II terminal..if any problems are in the engine, this will isolate..take!