What kind of GMC model is this?

I found this truck on Craigslist, but the description just says that it's a 1998 GMC. I would normally just ask the guy, but I also don't understand why the headlights look different than on most Chevy and GMC trucks. Why are the headlights a signle square instead of the usual two rectangular ones? When I look up '1998 GMC truck' on Google images, none of them have that style of headlights in the picture. I know that this is a silly question, but I'm wondering if the seller maybe just has the wrong model year listed?

http://i.imgur.com/uiqa72J.jpg

Its probably a work truck edition, or something similar.

This is listed as a 98 as well

http://imganuncios.mitula.net/1998_gmc_sierra_1500_sl_white_in_escondido_califor nia_1020005456687152377.jpg