I shot a Trophy Taker Pronghorn for about a year and a half. Throughout this time I would notice about 1/4 of my shots had the tail of my arrow going all over the place, and I would get bad groupings when I knew I had done everything right. Now when I say bad groupings, I mean an arrow 5 inches off at 50 yards, so no big deal, because that's still going to hit the boiler room on an elk. About a month ago, the rest broke, and I replaced it.
I picked up a QAD Ultra. Very similar to the Rip Cord code red. This rest is super easy to tune, and I've had zero off shots and no visable tail wobble on my arrows. And finally, my broadheads fly exactly where my fieldpoints fly.
Anyhow, my buddy and I were discussing it, and we figure that the pronghorn just wasn't getting out of the way fast enough.