I went on ahead and changed the fluid in my recently rebuilt T5 (WC). I put 500 miles on it since the rebuild without issue and replaced the initial Dexron III fill with RP Synchromax. I thought it would be good practice to change the fluid soon after the overhaul. I saw a lot of advertising for RP Synchromax so I decided to give it a go. The issue I’m having is with shifting into 5th when the tranny is hot. It grinds unless I shift slowly. I believe the fluid is getting too thin and slippery and the brass blocker isn’t slowing down to allow proper engagement. Is this a common issue with RP in a T5? Should I just go back to Dexron III and kiss the $50+ fluid investment goodbye? Thanks!