I'm not trying to be smart here but 6" at 90 yards doesn't constitute not liking xtp's. I shoot noslers, sierras, speer ,xtps, berrys and several local cast lswc (all hand loads) and 6 ' at 100 yards is a killing shot. Try using a silhouette deer target and shoot for a killing shot and shoot about
25 to 30 shots. let the barrel cool between shots when it gets warm and then see if it still is shooting 6". If it is go hunting. Look at the pattern-if it's drifting right, left etc. and make adjustments.
I use my tc barrel on one frame and an MGM 12.5" with muzzle brake on my other frame. The regular noslers and xtp's shoot best out of both barrels and out of my Super Red Hawk-9". The absolute best shooting bullet for either barrel or gun is Nosler 250 gr. partition handgun bullet. and that gets me 4-6 inches at 125 yards but much of that is old shaky hands and old eyes. Once again these are handloads but I don't do anything outside of the book loads.
If your only shooting targets then I understand your concern but if your hunting your getting it in there. If your hunting try adjusting your expectations and look at heart/lung/and artery/nerve bundle above the heart. Hit 3" to the right, left, up, down and the deer will never know or live with the difference.
Some of your play or fluctuation could be the type of rest you use, some could be trigger pull, some could be your forend is too tight or loose. You could get a trigger job, a custom forend or or a custom grip. I also use a trigger shoe
http://www.t-grips.com/index.html. they help my stubby fingers
