I just went through the same thing last weak. I changed (by I, I mean the garage) the plugs(NGK), air and fuel filter and cleaned the ERG and throtle body. Also replaced O2 sensor. These all helped, but the main culprit was the intake manifold gasket(big chunk of the gasket was busted off). Check that as well, it took me 3 trips to the shop to get it fixed right.

Good luck,
marc

99 rodeo 4x4 v6 80,000 miles
My Rodeo