Might be obvious, but check for loose screws and such. I had one of the underlug screws break off on my T/C Cherokee once. Suddenly the shots were nowhere near the target.
Shoot off of a bench rest and see if the problem continues. If it does not, then, unfortunately, the problem might be you. Get another shooter to try also and see if the problem is the same. If it is, then it is likely something about the gun.... cracks in the stock, loose/missing screws, sight moving in a dovetail, etc.
You always gotta hope that the problem is you. Flinching, bad sight picture, inconsistent loading techniques, etc. are all relatively easy to cure. Some obscure gun problem might have you pulling your beard out.