It's a lifted Jeep and can't speed? They actually buy that? Dang, what kind of cops ya'll got up that way?
One thing to remember though... if ya ever DO get written up, if you elect to go to court many times a modified vehicle will lose because the owner knowlingly changed it... take this from experience, I wrote all kinds of modified vehicles when I was a cop and it was pretty easy to get convictions.
As to getting the speedo right, it would be best in the long run to just get the right gear and install it so you don't have to worry about it any more.
Again the main reason being... if you KNOW it's wrong, and you are "guess-timating" as to what your speed is, they can zap ya if you get caught and have to go to court on that too. Their premise is you're relying on something that you know to be wrong so it's your problem.
All the ideas offered so far were good ones, don't get me wrong... I just wanted to offer some insight as to how the officer and court might be thinking should you ever get written up.
Later,
Chris