Alrite pal, few little pointers. first the turbo on TDdi`s dont start to kick in until 1600 rpm and dont full boost til 1800 rpm. with the car having over 200k on id say that either your maf sensor or ur intercooler senser has broken or dirty(the one on the left hand side of intercooler pipe). According to haynes manual the ecu uses both these sensors to decide how much boost to allow from turbo.(somethin to do how condense the air is extra).. I recently cleaned my intercooler and forgot to plug the sensor back in and it did exactly what urs is doin, itll go to any speed i wanted just took ages.(felt like drivin 1.1 lol)
Id personnally would start by checking both sensors and wiring, you twist them both anti-clockwise to remove.
Oh u can buy fords internal workshop manual off ebay (2.50) it covers all fords from 1993 to 2003 or sumfin like that well worth money.