F42 SUSPENSION... What this

I often browse autozone's online catalog for part prices and quite often I'm asked if my truck is with F42 SUSPENSION or without F42 SUSPENSION. I always assume I'm without or I would know. So what exactly is a F42 SUSPENSION. Whats special or different about this suspension?

according to GM's RPO database -

F42 : SUSPENSION SYSTEM, FRT, HD

Sounds like a beefier front suspenstion option, I checked and my truck doesn't have it.