Hi Proshadetree,
Im not familiar with this truck model and Im probably assumming a lot by thinking it may be like a Yale GLP30TF
This truck sounds like it has a very weak gasolene mixture and I would have checked all those points you have checked.
I simulated those syntums on a Nissan engine the other day as I was experiencing a surging problem on tick over, that the customer was complaining about.
When I examined the air filter I found it had an inner and outer filter in the same housing, Removing the inner filter aloud the engine to tick over but when I tried to rev the engine the revs would raise alittle and then die.
Dose the air intake on your truck go to an external vent in the safety canopy with a grill over it, if so block it of and see if the truck revs better, I know its really long shot, but you never know maybe the inner air filter is missing Dose this truck have a throttle pot maybe the problems there.

Titus