First of all Welcome to the forum!
Sounds like you've been firing a whole lot of rounds, so barrel break in shouldn't be an issue.
You also mention you had gotten a 2" group and a 2 1/2" group once, and that should mean that the rifle is capable of grouping, but then there is the question of how many rounds did you consider a group?
That is important because if that is the case, then it's not necessarily the rifle that is the problem, and it could very well be an indication that it's the scope, since the mounts you have addressed, but there is also other possibilities like not letting the barrel cool sufficiantly between shots, and the way you hold the rifle, the way you clean it, or not clean it, so as you see you need to take one issue at a time and I would start with the scope, and I say that because you said you did get a group or two at one time.
Let us know what you find, and if you've done everything and it's still not satisfactory, you can call CS and see what they say.