Ok so when the truck is under load or just drive, it idles as normal, but when you idle up and the truck idles back down it drops low enough that the truck starts knocking and idling rough, the only way to get the truck to run normal is to idle it back up and eased down to normal idle. Or by shutting the truck off. The oil pressure gauge drops off on occasion when this rough idling happens.
I was thinking the oil pump is on its way out, with it supplying the VCTs with not enough oil they may not be able to operate under such quick throttle changes
I would start with cleaning the throttlebody first. If it has build-up in it, the blade can hang sometimes and have trouble keeping a good idle. If it sticks a bit and the rpm drops too low, then yes the oil pressure can drop enough to cause issues with the cam phasers.