i have a viair (can't remember which one offhand but it was a bigger one) and a 3 gallon tank - seems to work fine with firestone bags... I'm not driving the truck yet, but have done dry runs with the suspension in the garage
got mine from suicidedoors.com ... I know i already bragged them up, but I really liked them and their prices
Engine driven is such overkill unless you're running 300 pound bags and plan on 'hopping' your truck. Please tell me you're not planning on hopping your truck...

 

if you are just planing to use the air ride to lower when you stop, or get over speed bumps then a small tank and compressor are plenty, the only reason i mention edc's is because of the noise a 12v makes, but under the bed of a truck shouldn't be that noticable, now in the back of wagon, you could feel the two vivair's pumpin

 

No Hopping here!!!!

 

yea i would stay far away from the aim products my brother used their switch box and valves in his s10 at first and they would stick all the time