Help with Fusion 1.4TDCI won't rev & lacks power

I've a 2006 1.4TDCI Fusion with 65k. Didn't use it for about 5 months (but did start it up regularly) then one day decided to use it for work. Fine for the first 20 miles. Then got a sudden loss of power, speed down to about 45 mph, ten minutes later another drop down to 30 then worse down to 20mph. There was a strong overheating smell, but temp gauge was normal. Pulled into a layby, checked under the bonnet for anything obvious then put my OBD scanner on - no codes. Called the AA out - he also found no codes, he checked that the turbo could rotate & messed with the fuel filter then pronounced that he thought the Cat or exhaust was blocked & recovered me home. I took off the turbo where there was signs of oil seal failure so fitted a new core thinking that would sort it - no effect. Dropped off the (mechanical) EGR, wasn't stuck open which would be the obvious problem, cleaned it up & refitted - no change. Swopped the vacuum pump and glow-plug controller with good used units. Fitted new MAF sensor & vacuum control unit (next to battery). No effect. Car starts and idles no problem. Blip the throttle - revs go to 2k then if you release the throttle  it struggles for 2 secs then usually resumes steady idle. Disconnected the cat from the rebuilt turbo to obviate blocked cat or exhaust - no difference. I've now bought a new EGR valve but not yet had chance to fit it and doubt it would make a difference. The only other thing worth mentioning is that at one point it started making a strange slurping/whooshing sound from somewhere I couldn't fathom, but seems now to have stopped this. Any advice would be very gratefully received as I'm now completely lost for ideas. Thanks!