I know its been drug through the mud... i have been researching for the last couple of weeks and have found no conclusive answer that i like. here's where I'm at. 2015 scat pack challenger. 6.4, m6. 28,000 miles. it's now 600 miles into its 3rd tranny. all replaced under factory warranty. yay, but im not satisfied with the trans. I plan on doing a barton shifter. but even with that, these sychros just suck. I know the vipers, corvettes, camaros, chargers and challengers all have the tr6060 but strictly speaking for the chargers and challenger, bc all others use different synchros, what fluid has made them behave the best? what fluids have made them worse than they were? I had read a thread where some people would praise RP sychromax, and redline D4, says it shifts like butter now, but those fluids are not recommended and will undoubtedly kill the synchros over time. Some people just shouldn't be allowed to mess with stuff. and i get the feeling that many of those kinds of guys are commenting throwing these unapproved fluids out there. i am considering: Royal Purple MAX ATF Amsoil Torque Drive Redline C+ and any other that you all have had luck with.