If it takes you an hour to go up 3 psi, then you definitely need a new/better compressor!!
When I had my Viair 2 gallon OBA, I could air up 4 tires from 13-32 in about the same time as it would take guys with a cig plug compressor to air up one tire.
I had to sell my Viair as I didn't have room in the TJ for it. I bought one that hooks up to the battery, and you just set the pressure you want, and it shuts off automatically. It's quick, but not as quick as the Viair. A buddy I wheel with has 37's, and uses the same compressor I bought. This is the one I bought:
http://www.canadiantire.ca/en/pdp/m...inflator-with-case-0095032p.html#.VwMJQBNViko