general problems of the 2001 GMC Safari

The engines revs up when vehicle jumps forward. One time, when driving to mailbox to retrieve mail, caused my arm to hit window frame and bruise. Four days ago I was behind a car at stop light. Jumped 3 to 5 feet. Could have easily hit vehicle in front of me. Brought to dealership for repair. Told me that it was a normal occurrence and to press hard on brake when stopped! this is ridiculous. I believe I was applying enough pressure and the engine shouldn't behave as though I have suddenly gassed it. I am afraid of this vehicle! don't feel safe. Also chokes when accelerating to merge onto freeway. Tried to trade in in Nov. Dec. But wanted me to pay addtional $3,000. Please help. Thankstried to.