Secret, the 98-99 Suburbans had leaf springs and the 2000 and newer have coils on the 1500's. A 1998 1500 should have no problem w/ 6000 lbs. They were rated for 7500 lbs with the trailer towing package which included a class 3 hitch and transmission cooler. If you are going to load the back of the truck with heavy luggage then have an extra leaf installed by a spring shop on each side s/b ~$200. So make sure it has the towing package. The 350 engine has a good amount of power.