I have a fault with my jag, I've had it for about 1 year. The engine revs fine when in idle but as soon as I start driving in either drive or reverse it jumps and has absolutely no power. Feels like it wants to cut out constantly. I've replaced the spark plugs and Upstream O2 sensors. Looked into the IMT valve but not sure if that's it either. But I'm not sure if its engine or trans as it only does it when in gear. PLEASE HELP!!