Maximum turbo boost shold come up at 1750 rpm if this is the same as the 406 engine so if its not giving good power until 2000+ there is something amiss with the turbo control, I think your only option is to get the fault codes read.

I had much the same problem a couple of years ago , i know very little about cars so please excuse my laymans terms, and it turned out to be a small plastic electrical component / valve i think they said , i was shown it but cant remember what its correct name was, but it was fitted in the right side of the engine in the air pipe its only about 2/3 inch square and cost £160 parts and labour at a peugeot garage. Ihope this is some help but i did say i know very little about cars. it may be a mba switch or lba something like that

I am having the exact same problem with my peugeot 307 2.0 HDi. I gave it a full service hoping this might improve the situation but did not help at all. Did u get any further answers on the problem???