Injectors usually won't cause that problem but the injection pump will. The only other thing that comes to mind is a bad exhaust restriction
NOOOO don't do that if you poor cold water on a hot pump you will ruin it.Dang, I was hoping it was going to be a simple fix.
One thing to try is when it's hot, and your having the problem, try shutting the truck off, and pouring water on the ip to cool it down.
If you start the truck up and it runs better then potentially your IP is bad.
Someone chime in if I'm wrong on this technique.