Rear Suspension problems of the 1997 GMC Safari

When starting up from park, the engine roars and looses power, sometimes only for a short distance but sometimes 500 to 600 feet. Also after starting up from a stopped position, the rear of the van gives off a very loud thud and van lurches at the same time as if someone rearended the vehicle. Sometimes, the van after being just started (still in park and not touching the brake or anything other than starting the engine) and sitting for a short while, the van will have a loud thud from the rear of the van and you can also feel movement at the same time.