Have a 2003 Voyager 2.4l that over the past few months has been bucking and when given more gas bogs down and starts to lose power. Back off on the accelerator and the issue either stops for the moment and returns almost immediately, or goes away for a little while. (hours to days sometimes) I just replaced spark plugs, replaced the valve cover gasket, upper manifold gasket, and throttle body gasket, as well as cleaned it as much as possible. Thinking this would help or alleviate the problem, I was wrong. Any ideas or common know reasons for this issue? Thanks.