This issue I've had for about a year, and started when I switched out the regular shifter for a Barton short throw shifter to help me shift faster. The shifts at first were clunk (normal for a short throw shifter) and I got used to it (shifts became faster). After a few burnouts with the new shifter, the transmission would randomly refuse to go from 2nd to 3rd when I would shift quickly. Instead, I would hear grinding when trying to push it into 3rd. I turned to my clutch as being the issue, thinking that after 30,000 miles driving hard and doing lots of burnouts that the clutch was probably slipping, so I went ahead and switched it out for a hellcat clutch. The stock clutch was severely worn down when I took a look at it, so changing it out was a good idea. However, this didn't help the clunky shifts or the grinding from 2nd to 3rd. The grinding happens from 1st to 2nd as well, but its not as common as 2nd to 3rd.