Are you using the clutch to shift or RPMs? Mine would if I clutched it, so I no longer use the clutch. With the 3. 54 rear end, I rev to about 2000 - 2100 RPMs then release the accelerator and shift quickly. never had another growl, grind, etc. How many miles is on the truck? As it breaks in, the gear clash will eventually disappear. The syncros just need time to break in.
Not any TSBs that I know of for us sixers. All I can say is play with it.