Problems with 81' 300SD
 

I finally started driving my 81' 300SD a lot because the brakes on my Audi are shot.
Anyways, it has a few minor problems I'd like to fix before they turn into something major. You input/advice is much appreciated.

- At around 45 MPH the card shakes bad, but not all the time and mostly when I just start it, it seems likes its in the front wheels because it jerks the steering wheel a bit, like an out of balance tire, but could it be a flex disk about to go bad?
- The heater only works when it wants to, some times hot fire, some times ice cubes. I have to keep messing with all the settings before it works, then it might stop again
- Its gets not so good gas Millage, Maybe 18-20 MPG with mixed freeway/city driving, and it has a lot of smoke. Im thinking the injectors just need a good cleaning or new tips
- Fuel gauge works some times, occasionally it stops at half and stays there other times it will read to empty. So I have to go by millage
- RPM gauge works once in a blue moon and bounces all around every once in a while
- The Sunroof doesnt work and is slightly open to the point water gets in if you go through the car wash. The previous owner said it stoped working when it got rear ended. I just either want to close it all the way or get it to work
- The rear sags, even with no one in there, Im thinking the shocks are blown
- It seems like it idles a bit rough, even for a diesel, once again I think this may be dirty injectors.
- The tranny doesnt always like to downshift from 3rd to 2nd and when it does, it will shift hard

Would like to fix all these as soon as I can, so thanks ahead of time for your wisdom.

Thanks
James