Hello again.

I'm currently having some fuel issues. When I fill up the tank, I stop as soon as the pump stops. I don't top it off. When I start it up, the gauge doesn't quite make it to the "F" mark. So maybe the needle is a little off, right? Well, the other day I was driving to work - 13 miles - and I was getting close to being on E. The station with the cheapest prices is close to work, and judging by the amount of fuel it looked like I had left - not quite on E, and the fact that with a full tank the needle doesn't quite hit F, I figured I'd should make it no problem. Nope. First time I've ever run out of gas. Or fuel in this case.
I filled up the tank and reset the trip meter. When the needle was at 1/4 tank, I had only driven 275 miles. Not cool. I'm averaging under 17 mpg. I compared it with highway mile markers and the trip meter and odometer are near perfect. Most of my driving is city, averaging about 40 mph and a little highway, mostly in traffic, but sometimes up to 75 mph.

Now then. There is a bit of black smoke. It seems like it smokes more than it should. I see a guy driving a 300SD on my way to work sometimes, and mine definitely smokes more than his. So what's this all about? I did a two can diesel purge less than 1000 miles ago.
Also, when I had the hood up the other day, I noticed that the banjo/alda line had come unplugged at the banjo. It was short and brittle, so I replaced it. I don't know how long it was unplugged. Could that lead to a decrease in fuel economy?
Also, I have significant flare between 1 and 2 and a little from 2 to 3. I try to manually shift it, but it's hard when you're trying to get going from 1 to 2. Could the flaring be burning a lot of fuel?
And finally, there's a crack in the downpipe. I'm not sure if that could effect fuel economy or power.
What should I do? Change fuel filters? The pre-filter is a little dark but not bad. The air filter is also a little dirty, but not that bad.
I'm trying to save for a WVO kit, but in the meantime I'm blowing all my $$ on overpriced diesel for a car with really poor fuel economy.

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1983 MB 300SD Turbo Diesel