Why does the truck sputters when under load?

Hello, what testing has been performed? What do the fuel trims look like? What happens if you "richen" the fuel at the intake manifold manually when the problem occurs? You could have an air intake leak. You could have an emissions controls issue. You could have an engine timing or compression issue. There's just no way to guess -- testing is needed. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops