I purchased a 1998 GMC Sierra SLE, which is lifted a little bit (I need a step to get in), did they come from the factory lifted if so how do I find out how much ? Basically for new shock purposes. (rough country)

 

Perhaps oversized tires. I know my own truck has oversized tires, and me being 6'2", I have to step slightly more up into the truck.

Where I would look, is under your rear leaf springs, on top of axle. This is by far the easiest place to install a lift on the truck. These lift kits range from 2" up to 4" and they're just blocks of metal that raise leaf springs off of the axle with longer U-bolts.