Is this a scoped rifle? A lot of times a rifle takes time to break in or the shooter time to get used to the rifle but it sounds like you covered all that. I would suggest some loose powder. Start at 90 grains, shoot a group, and then swab. If you're not happy, add five grains and shoot another group. Also don'r forget to try bullets other then a Shockwave. Maybe some XTP's, Gold Dots, Nosler, Barnes, even powerbelts...

Welcome to the forum and good luck.