There is reason for the the speed limiter on a truck. Its a truck not a race car, unless the suspension is modified (for the better) you shouldn't be going much faster than 75-80. Trucks are light in the ass end and not very balanced when unloaded, so they become somewhat unstable and touchy at high speeds. You may think you are in complete control but the a small bump at high speeds can have a big affect. Reality is, you dont have nearly as much control as you think you do.
With that said. My record is 120 downhill with the wind in my 95 on 33's. :

and it got to that speed faster than the Neon beside me.lol