I use the firestone airbags with my 2112 GMC Sierra 4x4 It does really need much air to make it level 30lbs or so.
I have the model with the pump and gauge under my dash.....This works well on bouncy roads and I just add a little more air to keep the trailer from bouncing.
I also had these on my 2005 silverado and they really made a great difference in ride...The silverado bags did not fit the 12'GMC so I had to buy new bags.
I recommend them foe excessive hitch weight.
I have the nearly new bags if you would be interested the fit 1998 to 2007 GM trucks and need abou $10 of fill tubes to complete.