Low power syndrome (again) longwinded

[rotory]

2004 Mk6 Ford Transit 2.4 TDDi power mystery !
My super duper Transit(Di) Motorhome has developed the usual hill climbing problem. It is sluggish to the point of being unable to climb hills or the slightest slope without going through the lower gears. Once at the top of the hill and on the flat it goes like a train, up to 70mph.
I've cleaned and inspected the whole air system , new filter, cleaned intercooler, cleaned EGR, cleaned the inlet manifold, Turbo cleaned and ok. All pipework inspected and cleaned. Fuel filter replaced with Ford DI filter. Housing ok. New Timing solenoid installed on the pump 2 years ago. MAP sensor replaced, no MAF sensor fitted.
But,
When I first start the engine, I dip the clutch, rev momentarily to 3000rpm, release clutch then rev momentarily above 4500rpm. It then goes like a train. Or for my next trick when the engine is cold, I remove the vacumn pipe from the EGR valve do a few huffs and puffs on the pipe then replace it , start the engine and it goes like a train again.

I'm now thinking that I might have a duff vacumn regulator solenoid. Only other thing I can find is the connection on the back of the vacumn pump seems to be slack....
Any theories.......thanks Martin