when i push the gas my explorer hesatates to go, it goes very slowley then the rpms go up to about 2 then i have to let off the gas some to let it shift, it shifts without a problem once i lewt off gas but it wont go very fast at all,, only if i go down a hill and pick up speed.. but when i go up a hill i loose speed.. changed plugs and wires, put new coil pack in it. changes erg valve.. nothing is helping it and its very aggrevation, cam u please help..