Forgot to add: I am really starting to loath the standard rubber valve stems. If anybody has any good upgrades for stock steel dually rim valve stems, I'd love to get something better than the failure prone rubber versions.
Standard stainless stems can be had from just about anywhere; Amazon has many choices.
Installing them is simple and I would be ashamed if I had to have some air-gun guru tire jockey install them.
Lay the wheel on the concrete/ pavement (or a sheet of thick plywood).
With all the air out, put the foot of your hydraulic bottle jack on the sidewall against the rim.
Don't have a bottle jack ----- you need to visit Harbor Freight and remedy that situation quick...
Of course you are doing this under something heavy like the rear bumper of the truck or a gooseneck trailer or a dozer blade.
Raise the jack against your heavy item and carefully keep jacking while the foot of the jack presses the bead of the tire loose from the rim.
Once the bead is loose, slide the wheel out from under your heavy item where you can work on it without bumping your head.
Smash the sidewall down out of the way and cut the rubber stem out.
Slather some rubber lube or vegetable oil or cooking spray on the appropriate rubber seal that came with the new stems.
You should have gotten two seals per stem, a 5/8 and a 1/2; used to, everything was 5/8; but, for the last forty years, most things are 1/2.
Put the seal on the stem with the little ridge up; this little ridge, 5/8 or 1/2, goes in the hole in the wheel.
Poke the stem up through the hole and add the stainless washer and nut.
Snug the nut down with your Deep Well 9/16 socket.
No need to try and hold the stem from turning, when it gets tight enough to want to turn the whole thing, that is tight enough.
Slather some of your lubricant all the way around the tire bead and air it back up.
As we are talking about valve stem extensions and all the various attachments one may have on and between dual wheels, I highly warn against allowing any tire monkey anywhere around the wheels; they can do more damage and cost more money in a few minutes than I can make in a week --- best to do all your tire work yourself and leave the shiny pit-crew airgun locked away; airguns have no place around wheels and lugnuts --- ignore this at your peril.