I know my response is WAY late on this one but for those that do not know.
I have a 1989 GMC Rv model (not the K model made the same year) 2500 HD Suburban and called the GM Customer Service number and they told me exactly what my towing capacity is. I made the call back in 2006 and would be willing to bet they still have those records today (2009)
Note my suburban has the 350 not the 454.
I was told it had a carrying capacity of 3,000 lbs, Towing of 8,000 lbs. GCWR of 13,500 lbs and an approximate curb weight of 5000 lbs but probably more like 5500 lbs.
So you can bet for sure the 454 can top that by at least 2,000 or 3,000 lbs.
But CALL the GM Customer Service and ask them. They will want you to get some numbers off a sticker on the inside of your glove box door and they can tell you exactly what the towing capacity is if it is unmodified by any previous owners.
The 1989 R2500 Suburban is an excelnt towing vehicle. Strong, Durable and dependable.
I highly recomend one to anyone. I can't say anything about the newer models but the 1989 RV model is exclent.
Just make sure you get the rear breaks adjusted frequently. They tend to not auto adjust unless you know the trick to get them to auto adjust. Even just backing and breaking doesn't always adjust them. You set the emergency brake so that is just bearly touches the drums then back up and hit the brakes hard. Not hard enough to lock up the front tires but almost that hard. That should adjust them. I do that about every month or so.
1989 GMC R2500 HD Suburban.
Airstream Cruiser Travel trailer (The Runaway Sue)