I drive an 87 4000 with a 1.8 engine. Almost as soon as I start the car, the gas guage raises to the highest point and remains there - it doesn't matter how fast or slow I drive - the car runs fine. On some of my other vehicles 84 4000 and 87 5000 the guage will indicate different pressures depending on my speed - Is this a problem I should be concerned about? and what can be causing this?

You are mixing apples and oranges! Audi's don’t have a factory fuel pressure gauge, it's either fuel level or oil pressure. If it is oil pressure than most likely it is the sender, an open or corroded circuit will peg the gauge.

i have three guages on my console -amps on the left and oil temp in centigrade on the right. The center one - which I think is fuel pressure, is indexed from 1 thru 5 and is measured in bars - if its not fuel pressure, then what is it?

The three gauges that you are referring to, if they are factory stock, are the oil pressure, oil temp and volts.

the three guages ARE factory - although I have seen 4000 models that use the same plastic mounting with the center hole molded flush and only two guages, oil temp and amps

I have seen some older models didn't have oil temp but a clock instead.