No power below 2000rpm on an old(1998) L series?

Hi all my poor old 400 GSDi has been getting slower and slower over the years which is pretty normal I guess but more noticeable recently. At the weekend was lost in Reading town centre getting pretty hot and bothered (as was the car!) and had literally nothing below 2000rpm and not much more above that. Journey home was pretty much foot on the floor all the way to keep up with traffic. No smoke, no funny noises etc...

Now I'm sure no power at low revs in normally MAF sensor but isn't that just on the later models 25/ZR + 45/Zs?

Throttle pedal sensor of some kind?

Any thoughts?

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