The grey smoke may be nothing more than the valve cover gasket dripping on an exhaust manifold. My Spirit smoked badly because of this with almost no oil consumption, you'd be surprised at how far a little bit of oil will go when you're making smoke. Unfortunately, the rear bank's valve cover is crammed up against the firewall. The 35mph limit sounds like you're in limp mode. It could well be a sensor, but we'll need codes to know.