Could be water in the gas like the first reply said. Also, I remember someone describing symptoms like that when their fuel filter was clogged. I change mine about every 20k because the gas around here can be kinda questionable sometimes. Maybe just try changing it and see if that helps....its not expensive and won't hurt. The other thing I can think of would be your fuel pump.
But try the filter first, esp if its been in there a while.
