I would not see an issue with 6500 lbs. That is what the average joe (myself included) is looking at with the typical Jeep/compact 4x4 on a 2 axle flatbed is likely pulling.
As mentioned, some airbags or timbrens in the back if its sagging...
I've had several friends in our club pull with burbs, tahoes, and K1500s of that era with no trouble.
In the immediate, the power of a 13 yr old 250hp small block is your limiting factor. Int he long term the 4L60e is the weak link. Make sure to keep it cool and maintain it.