Got a 1992 300D 2.5 that just feels down on power. WAY slower than my 300D 3.0, it has trouble getting up hills. Just feels like there is no boost. It jumps off the line but about 2k it's worthless, up where you'd expect the turbo to take over.

What should I address before I decide the turbo is bad?

Air filter was pretty nasty as was the oil. Change of both made it marginally better.

Will bad fuel filters make this huge of a difference?

if fuel filters are dirty, you don't get fuel to go with the turbo boost pressure... air don't burn.
next on the list is the alda fitting on the intake. it's just about directly above the IP, and it's a vacuum line looking thing with a crimp fitting on it.
it should pull right off. look inside the fitting and see if it's clogged. if it is, you ought to pull the intake and crossover and clean the bejesus out of it. *(egr sucks...)
look those over, and report back here.
you have your orders soldier.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I'll be going back down to cincy in two weeks to work on the car. I'll look for that fitting. Its got 202k on it so its probably nice and carboney.