I usually recommend Synchromesh for stock cars and 75W-90 GL-4 for tuned cars. I recommend 75W-90 GL-4 where people have 1-2 shift grind issues. I recommend Synchromesh where the weather gets quite cold for much of the winter (below 0 F). Both will work, and I've swapped back and forth repeatedly.I have a 2011 cruze eco MT and I've been looking on the forum to troubleshoot some grinding and notchiness issues I have. I'm not sure which fluid to use, it seems like every thread uses these terms interchangeably. Do I need the AMSOIL 75W-90 GL-4 or the AMSOIL Syncromesh 5W-30?