Weird Vibrations

[Jbrack96]

So I just bought a 2013 Chevy Silverado crew cab w/ 118,000 miles on it, and recently noticed a vibration that seems to only occur at 10mph or lower when braking and not braking. I feel the vibration coming from my rear end so I suspected that I should check my rear diff fluids because maybe it could be too low but after reading a forum similar to this I'm not sure that's the case. I do know that my current M/T tires are pretty worn and out of balance so that could possibly be the issue, but I want different opinions from you guys before taking it to the shop, if I can fix it myself I would rather do that, thanks.