I have about 108K on my 2006 Box and decided to change the trans fluid last Sunday. Everything went fine and replaced it with Royal Purple Gear Max 75W90. Wed came and I started to grind shifting from 2nd to 3rd, which has never happened before. I used exactly 2 qts, per the manual. I went ahead and picked up a few qts of Redline MT-90 and am thinking about pulling the Royal Purple out and replacing it with the MT-90 this afternoon.
according to the RP specs, it is on the thick side of the 90w. I'm sure ur problem becomes more obvious when initially driving rather than when she's warmed up already. Go with a thinner side of the spectrum oil like the AmsoilSynthetic Manual Transmission and Transaxle 75w-90 GL-4 (MTG) and you'll never look back. Some have had good luck with the eneos 75w-90, personally I haven't tried it but if it is thinner than what you have right now it should work as well.
Actually, when I first took the box out this morning it felt notchy going into 3rd but no grind. Once she had a few miles that when I was getting a grind into 3rd. So, I would shift into 4th and skip 3rd if I could.
Just drained her and I'm going to wait a bit with a brewski. Then fill back up and see what happens. Royal Purple called me back and said they would compensate me for my "issues", and they had another report of the same situation. Additionally, O-Reilly auto parts said to bring the Royal back for a full refund and they would send it back to Royal for analysis.