I'll be placing my order for my Pac Brake with upgraded compressor (625) and bigger air tank.
Has anyone been able to mount a 5 gal tank on a 3rd gen short bed?
Mine is a manual trans if that makes a difference.

 

Go to a local big-truck wrecking yard. Find a small-ish aluminum tank. The size will be obvious, when looking at a pile or rack of tanks; it's just a few inches smaller than a regular steel tank. Be sure to grab the tank mounts too!

It should fit right between the frame rail and lower part of door trim. I put mine on the passenger side. There is one pinch rail that needs a little bend to clear the tank.

Tony