I tried both the RE trac-bars at various times. With the standard duty one, I didn't have any problems at 3.5". Lost that one in a wreck and replaced it with their HD trac-bar and mount. It drove really nice because the mount lowered the point it mounts to on the frame and made the bar more parallel. At 3.5" though, the HD trac-bar hit the diff every time I flexed, so then I went to a Tera-Flex trac-bar. The Tera-flex doesn't lower the mount point like the RE HD one, so it doesn't feel as good on the road, but it's arched so it misses the diff no matter what lift height you have, and it's adjustable without removing the end, which makes it easier to center the axle when the trac-bar is already installed, without having to remove and put it back on several times to get it right. If I had to buy one again, I'd probably try Skyjacker's, because it raises the mount point on the axle, and thus runs more parallel and should have a better feel to it, and since it runs from the top of the axle, it shouldn't hit the diff like the RE one did. Just my $.02 if you're looking to upgrade since you have to replace.
