got no power in my td!!

my 1990 td 110 csw has started to lose power again! before it was a warped exhaust manifold stopping the turbo from spooling up, but thats working fine now and had done since job was done but recently its loosing power again. there are no signs of head gasket failure and only smokes a bit on start up. engine has done 40k ish since turners rebuild. no alarming sounds from anyway but the temp rises pretty quick on hills. not useing oil and water any more than expected and no signs of cross contamination.

any ideas guys?

When does it lose power, at high revs? Air filter good, not wet?

Lift pump, blocked fuel filter???

loses power when going up inclines, basically when its under more load than on the flat. starts dropping off as soon as you start climbing.
airfilter is brand new and breaths through a snorkle . just had a full service as an attempted fix so symtoms started before that.

cheers.j