I know the Tremec T56's made in Mexico from 1998-2004 are somewhat weak on forks and synchros...at least compared to the T56's that were built in earlier years by Borg-Warner. I don't know if the quality has improved since then. If using one of these I'd insure that all the earlier weak links were taken out on the rebuild. To me, T56's can be a litte rattly with various whines specific to each build. I don't know what quality the factory is putting out on these for new aftermarket builds. Other than for highway cruising at >65 mph the 6th gear (with 3.55 or lower ratio) has limited use. I have 3.42's and 1st through 4th covers about 98% of all my driving. With real stiff rear gears 5th and 6th probably become a lot more handy. I know that having that extra 6th gear slot has lead to occasional missed shifts in either direction. My favorite is going from 3rd to 6th and losing all power. And 6th to 3rd at highway speed to climb a hill can be fun too, though pretty rare. Sometimes I wish 6th weren't there so those 3-4 or 6-5 shifts weren't as "missable."