In lieu of the post above I would like to state I am not in total agreement with what Tremec is saying. I beleive the reason for their caution is the fact that so many of the aftermarket shifters are mis-adjusted and do cause problems with their transmissions so they feel it best for them to be left out.
I can't seem to remember inside the 3650 there even being a shift stop on the 3-4 gate assembly, only on the 1-2 gate assembly and 5th gear shift fork. That said, even if there was a stop on all of the gears what is stopping the extra pressure that is being applied to the shifter turret assembly and the nylon piece mounted on the shifter ball that is inserted into the socket of the main shift selector rail? What about the pressures that are applied to the selector arm which determines which shift rail is selected? These are all before the stops used in the 1-2 gate and 5th shift fork.
I use the stops and I make sure they are adjusted properly like the Shifter Manufacturer's are instructing the installer to do. I use a .010" gap gauge for setting mine up, by putting force againt the shifter towards the 1-3-5 direction and adjusting to a slip fit gap of the .010" gauge and then doing the same on the 2-4-R side. I always make sure I use locktite on the stop bolts and the stop bolt lock nuts to ensure that nothing will move and become mis-adjusted from viabrations.
I do bang the gears hard sometimes and the amount of flex that is applied during those shifts will flex the internal parts enough to allow the .010" gap adjusted into the shifter to be used up and hit the stops on the shifter assembly. If one never plans to speed or power shift would be the only reason that I could see for leaving the stops out of the aftermarket shifters.