Your car should do better than 90, easily. I saw 92 _in traffic_ the other day! Ok it was a fast crowd. On the kickdown, I have noticed that mine won't kick down if I'm going faster than 65 - 70 or so - I have not done a scientific test to see the point at which it won't kick down.

If you floor it from a stop, at what rpm does the car shift? It should shift somewhere around 4800 - 5100 rpm. If not, something is restricting fuel flow.

I would have guessed your issue is fuel filters, but you said you changed them. If you do take your manifold off, change the plastic fuel lines as a "while you're in there" thing. If you see bubbles in the fuel lines when running, you have an air leak somewhere.

The yellow film is "cosmoline" or whatever they put on your car new to make it look nice, but it yellows on age and is very difficult to remove. BMW's have the same thing. Unless you are a detail person I wouldn't fuss with it.

About the vacuum line, on my car there is one "tube" with 2 lines in it running behind the dipstick.

Rgds,
Chris W.
'95 E300D, 258K