Well, p0243 is a wastegate solenoid - is it possible to change it separately from the turbo?

Yes it is possible to buy just a solenoid, as it sounds like the solenoid has failed, but they are not cheap. Do you have any mods on the truck, or is it bone stock? There may be a better way to go about it..The part number is a Holset 4036054, thou I can't find any online.