Mercedes Benz repair: My mercedes still wont climb hills, fungus problem, line leak

Question
I have an '80 300 SD with an automatic trans.  I have been having trouble climbing hills.  If the engine bogs down and I have to downshift, sometimes it's fine and will work great, other times it's like the engine has a governor on it and will not accelerate beyond a certain RPM until I pull over, put it in PARK for a few seconds, back in gear, and then it will work great.  It's worse if I have to downshift into 2nd.  It's not so much of a problem in the higher gears.  I have cleaned my ALDA tube or whatever it's called, the banjo fitting on the driver's side of the engine.  

Answer
Best guess:

#1. Plugged fuel filter = possible fuel fungus problem
#2. Fuel primer pump leaking
#3. Fuel line leak
#4. Turbo failing, very rare.

Diesel Injection:
http://www.mercedesshop.com/shopforum/showthread.php?t=142405

Diesel Fuel Delivery:
http://www.mercedesshop.com/shopforum/showthread.php?t=142399

Engine Mechanical:
http://www.mercedesshop.com/shopforum/showthread.php?t=142400