If your boost controller was bad, you would be on pure wastegate spring pressure, which is probably around 7lbs. So highly doubtful it is your controller. If I was in your situation and I was getting as close as .5lbs from my target, I would guess that it's nothing major mechanical and probably in your tune. I would put a couple turns on the wastegate actuator and run a log, it's not going to hurt anything. I would not be looking for ghosts on such a small amount of boost, even 2lbs at 5k isn't really telling us much. I tried to open the tune but never got the defs to work properly, I am still a bit concerned with why the ecu didn't try harder, but as long as it's not totally whacked and is doing it's job to a certain extent I would adjust the actuator and see what happens. Go in baby steps and log each time, I would get where it's within .5lbs consistently in 3rd and then do a 4th gear pull to 3800 or so and make sure you aren't spiking.