2004 Ford 6.0 in a F350 srwd / 4 wd crew cab pick up
Truck seems to go into limp mode while pulling travel trailer up a resonable grade. 75 mph to 30 mph almost instantly.
Wife says she hears a high pitched whine just before problem occurs.
Had problem before and after replace EGR cooler, Oil cooler, Turbo, High Pressure oil pimp and High pressure fuel pump.
Have a Trans temp guage and it is the normal range, Boost drops to below or at 10 lbs. and exhaust temp is at normal.
There are no codes logged as per the Ford Dealer.
Above repair work was done when I lost EGR cooler (while towing)
I need suggestions. It is a great truck other than this towing issue which seems to be getting worse and even slight hills seem to sometimes trigger this condition.

 

check the plastic intercooler pipe on drivers side if this is a late 04 truck, early 04s will have a metal tube. they can crack and still be able to build some boost but when it gets to high to hold it will bleed the pressure off and it will make a screaming wistle sound. also check all your intercooler boots, especially the one that makes a 45deg bend right at turbo