Sorry to be a 'Johnny-come-lately' to this problem, but I might have a solution to this problem.
What it sounds like, to me, is that your camshafts may be in a retarded positon by one or two teeth, causing the poor performance. You could also have a problem with cam phasers that are not advancing the cam timing during acceleration. These problems would not be apparent in no load acceleration (transmission in park or neutral), but would be very apparent in acceleration under load.
I would definitely have both the camshaft timing checked, and have the cam phasers checked for proper operation.
I know, from personal experience, that when the timing gear started to go out on one of my previous vehicles, the cam timing retarded one tooth. You used to be aable to tell this because the initial timing woudl be retarded when read from the balancer with a timing light. You would then advance the initial timing by resetting the distributor, and everything would seem fine, until it jumped another tooth and retarded the camshaft further, and even then with the timing reset, the engine would be very weak.
Hopefully, this information will help you get your truck back to 100%.
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