One thing at a time.

Let's get the motor going, then address the transmission.

Diesels don't jump off the line like gas engines. Expect 0 to 60 mph in
about 13 - 15 seconds. That's when it was new with say 25,000 miles.
We'll do the best we can with 200K miles. In the order of complexity and
work:

1. Is the exhaust laying down a smoke screen? If so check the paper air
filter element; it probably needs to be replaced.

2. Check the throttle linkage. Have a helper sit in the driver seat with
the motor OFF and floor the throttle while YOU watch the movement of the
throttle levers etc. especially the one that goes down behind the
injection pump.  The lever back there should touch the full throttle
stop when the helper floors the pedal. If it doesn't adjust the twist
rod near the firewall so that it does touch.

3. At the very aft end of the intake manifold, near the firewall you'll
see a plastic tube attached to the manifold. With the engine OFF remove
the (hollow) bolt that attaches that tube and clean it out with a paper
clip wire, also clean the "banjo fitting" that the hollow bolt secures.
Reattach them. Then follow that plastic tube to ensure it's connected to
each fitting all the way to the injection pump. If not, fix the break.

4. When were the motor's valves last adjusted?? Due every 15K miles. If
they're neglected the motor has less compression making starting harder,
especially when the weather is cold, and less power. You can adjust them
yourself, it's done with the motor OFF and cold, not hot. Takes some
time and patience.

5. Look at the injection pump - at the place where the plastic tube from
the intake manifold attaches. It's a square with a circle and an
adjustment screw in its center. Does it look like someone tried to
adjust it? (Pray they didn't.)

6. The turbocharger should put out about 10 psi boost at 4,000 rpm under
load (driving). It has a pressure relief valve (wastegate) to ensure
that pressure is not exceeded. Turbos last a long time so the turbo is
probably OK.

Check these items and pose the next questions. Next post given an
opinion whether or not anyone has messed about with this motor.

Transmission: Designed to shift hard at full throttle and softly at
moderate throttle so it sounds like it's doing just what it should.

Clean out the banjo bolt fitting. There's be a clear hose at the back
of the engine stuck on a brass bard on the intake. It gets clogged with
good and can't do its propler job of telling the IP to dump more fuel
into the engine when the turbo is spun up resulting in great slowness.

Just clean it out and you should notice an instant and dramatic difference.

This is fairly common. If the hose is not attached you'll have a 100% non-turbo
car.