Weak suspension, What sould I do?

Hey guys, fairly new on TW. I have a problem, the rear springs are not strong enough to hold up the 450lbs. of equipment I carry for work daily. I have installed hellwig 981 helper springs(1200lbs. rating), but the driver side has broken twice. On third set, but does not keep the rear end from saging 2"-3". Also have rancho 9000 shocks on rear and the rancho 9000 qwick lift on front to level the truck. Set up seems to work good when unloaded, but sucks loaded. I thought about adding firestone ride rite air bags with in cab controls for quick adjustment for loaded and unloaded. Or, should I do something like Icon's aal and front coil shocks (think it's stage 2 kit)?

 

This: http://www.tacomaworld.com/forum/suspension/194386-tacoma-spring-refurbishing.html

 

Thanks for the link.