If the truck has plenty of power, I would lean toward the speedo being off. It could have had the tranny or rear end changed. BTW,,,, How good are your brakes
There is enough good in the worst of us and enough bad in the best of us that it does not behoove any of us to criticize the rest of us. - - Be yourself. If you are ever lost, It will be much easier to find yourself if you know who you are!