I am running both shims since I got the truck in 2011. They didn't seem tight when I assembled them initially. I have rebuilt the diffs a few times to put fresh grease(by the way Marcus recommended it over oil and I have to say it turns to oil after a while but haven't had a leak yet, Kyosho grease is awesome)and the gears were fine. I had a clicking noise and went through the car and found the front pulley bearing went bad (my mistake, I put the pulley on backwards), haven't heard the clicking since. But there are a few guys I know complain of it, so that's why I am commenting on it to further understand. My diffs have all the shims and work, wonder why the problem....when you guys take the outer shim(the shim outside the diff-case let's just call it that) off, do you have any end play on the out drive?