Same exact problem on my 03 GMC sierra 1500 2WD with 110,000 on it. I have changed my rear struts one was leaking, just did my U-joints today, trans mount and changed out sway bar links and bushings. I got brand new tire 10,000 miles ago and changed my rear diff fluid . I have had my truck up on a lift a few times and have inspected everything on it, I have no play in my front end but my upper driver and lower passenger boots are ripped. What i have noticed is that it does it when everything is heated up in my truck, I did the neutral test and the vibration is still there I really don’t think it will every go away.