I just installed a set of 5.13 gears. What a difference My JK really takes off and I feel alot more confident passing cars. Better than stock by far

Now heres the problem: I get a mild to moderate vibe sometimes a with a ocasional knocking noise when traveling around 10mph and only at 10mph. I feel it when I accelerate and when I deccelerate. Basically every time I pass through 10mph range. If I keep the 10mph speed I can maintain the vibe. What could this be? It didn't do this during the first 3-5 miles or so. My only suspect is the rear pinion oil seal. The reason is that the over haul kit that I ordered came with a pinion oil seal that didn't fit properly and we couldn't find any that was for Dana 44. We found one for the Dana 60, so we put that one on. I have to admit that it wasn't a perfect fit. After the first 2 miles or so we parked it and waited to look for leaks. No oil was on the floor, but the seal was wet with oil. We plan to change this seal for a Dana 44 after the weekend. Could this be the problem or is it something else?

Please help