Things seem to be getting worse by the week....anyways, I've been noticing that as I am driving along in 5th gear, there is usually a rather strong and hard vibration felt in the car and especially the gas pedal, when I reach speeds around 120km/h-155km/h, regardless of my RPM or how much pressure I put on the throttle. To add to the confusion, [I may be wrong on this, but...] I don't recall this happening while in 4th [or any other gear], although I usually don't past 120km/h in 4th all that much. As well, there is no problem doing speeds lower than that in 5th. As I have just but the car a month ago, and am new to stick shift, I'm not sure if this vibration is normal, BUT I strongly doubt it is, b/c it is a luxury car, and also I had the exact same car, same year, same engine, but with tiptronic, (1998 Audi A4 2.8Q 30 Valve) and at speeds over 200km/h it was nothing close to as unstable. To clarify, the RPM's remain in regular ranges and never reach near the redline when the vibration occurs, and I have had my codes checked recently, with no errors showing [other than O2 sensors]. Any ideas???? [The vibration definetly seems unusual, however, just to be clear it isn't all that bad- its likebeing in a stock neon trying to push 200km/h, but it is definetly noticeable and sometimes loud]

In Addition; if it is in any relation to the above, my tires may be unbalanced and in need of some severe pumping b/c I have had trouble getting the to pump properly, so it may have to do with the tires.......but it seems unlikely.....

Get your wheels balanced. If it is not rpm related and only speed related, thats probably the problem. Unless your under cariage is coming lose (control arms/tie rods, etc.)

+1^

I also agree

Defanitly. my tires were unbalanced. between 70-85 MPH it vibrated. take it in. its a cheep quick fix. and itll feel soo much better when its done.

Actually, its very likely the cause of your trouble. And also the cheapest, first thing you would try when troubleshooting a problem like this.