Update 2 - had the injector fixed and this weekend did the trip up to Banff pulling the 5thW. Truck has run fine since it was fixed when not towing BUT the dreaded wrench came on again when I was on the way out of town!! Pulling fairly hard up a hill. Disappeared again when turned off and on again.
On the way back driving the same roads/hills I decided to not let the turbo psi get over 30 - and NO WRENCH and power down!! Truck ran smoothly all the way. Not exactly sure what that means but will continue to monitor and get fluids changed as I can afford it.
Cheers,
DR