I just bought a lifted '99 Yukon. This is my first lifted vehicle and I know basically nothing about how it all works. I've noticed that I get a lot of vibration at low speeds starting at about 15 mph until 30 mph. It feels s lot like the tires aren't balanced but then it gets better as I speed up and smooths out completely once I get past 30 mph. Any ideas on what I should start looking at?