Being a long time driver of over 20 years and having taught people how to drive for a few years I can honestly give you some good advice. 1st of all, always use a clutch, there is a reason why they put a clutch in these trucks that are manual shift, alot of old time drivers and some new ones that were taught by the old ones will not use the clutch which will work to shift into gears but will wear down the plates after awhile.
Now, to up shift you know that you have to get the rpms between 1400-1800 to shift without damage to the transmission. The same goes with down shifting, you need to get the RPMs high enough for the plates to line up, but dont think that you can rev the motor up to 2600 rpms and the truck will downshift, you have to be slightly higher than when you started, so if your tach. 1900, then you need to push in the clutch, let it out at the same time your shifting into nuteral, then tap on the fuel petal until it hits 1900 2000 rpm,and at the same time press in the clutch and pull it down to the next lowest gear, repeat steps until you get to 6th gear, now you have to push the button down that is on the shift handle then repeat all the steps I just told you and remember when you upshift again to push the airride switch back up again.... I hope this helps you but my greatest advice would be to buy a truck with automatic transmission.. I can not figure out why these companies buying new truck dont buy them with auto 10's, greatest thing since sliced bread.......