'99 durango with a few problems, need help

We recently replaced the head gasket, intake manifold gasket, and exaust manifold gasket. Truck still has exaust leak, idle drops below 600 and fluctuates up and down (wants to die out) at a full stop in any gear. On take off, the truck "sputters" acting like it doesn't want to go and it takes pressing and releasing the gas pedal several times before it finally drives normally. We have no clue what the problem is:banghead:. Truck has 5.2 V8 and 160,000miles on it. If anyone can help I would greatly appreciate it. Thanx in advance.

Does the exhaust leak still sound like it's at the exhaust manifold? Could be the manifold is slightly warped?
If you have a partially plugged exhaust system you could have all sorts of power related problems and even leaks at the manifolds. Have you checked to see if the cat convertor or muffler is plugged up?