89GT351

Hello, I have an 89 Mustang with 351W motor a one-year-old 5 speed Tremec T5 trans. With 6 puck clutch and adjustable clutch quadrant. The problem is with the trans. When I shift the gears at high RPM (3000-6000) from 4th to 5th it grinds If I shift at around 2000 RPM or lower it’s fine. I tried adjusting the clutch cable making it lose and tightening it all the way and it still grinds the gears. I did not have that problem before, it just started happening about a month ago or so. Does anyone know what might cause this? And how do youfix it? Any help will be appreciated.