Ok so I got some issues with my 99 wrangler sport 4.0. First off my speedometer is off by ten miles and hour. How can I fix this? The other one is since I bought this jeep I've replaced the exhaust manifold because it had a giant crack. I could literally twist it off the exhaust with my hands. Anyways just installed the new one everything went fine, its quieter and I'm getting better gas milage but I'm not sure I'm getting all the power out of it that I should be it's very hard to get it above 60 miles an hour. Anyone have any suggestions.