air ride... not enough lift!

[sqweaka]

hi all, ive added a budget air ride setup to my 49 pickup, ive 6" firestone bags up front in a jag cross member and 110 sleeved firestone rears on a four bar setup, i bought a kit of ebay to operate it, 4 gallon alloy tank, single viair 444c compressor and 4 paddle switches, 2x viair twin needle gauges, the tank came with a 110/145psi pressure switch, oh and 1/4 air line.
in operation with a full tank, by putting everything in the front first till it stops lifting (120psi approx) then whats left in the rear (40 psi approx) i can get the truck up to ride hight.. just about, but in reality often there isnt enough to get it of the ground, and i have to wait till the tank refills to get clear of the ground
i had a spare 2 gallon tank which i added inline with the 4g one but to be honest it made little difference, is a higher pressure switch the answer?
the tank is rated at 200psi, but i have heard that the viair pumps are good but the check valve do fail!
any advice please