Oil pressure issue...Sludge, sensor or other?

I have been searching all of the VW sites to find the cause of my issue and all I've come up with so far is that it could be one of many things. I know someone out there has the answer.

Ok...here goes...I recently bought a '01 passat GLS V6. It has 145k miles and is in pristine condition from all angles. I have worked on cars for several years but never on imports and mostly pre 1998 models...so I'm kinda unfamiliar with all of the computer controls that this car has. Anyway, After the passat is friven for 5 or 10 miles and is warmed up, the Oil Pressure Warning light comes on advising me to stop the car immediatly. I have seen a lot of people have this problem but it seems to be somewhat random in their accounts. With me it is specifically after the car is warmed up and only comes on when the RPMs drop below 2000. If I accelerate and raise the RPMs over 2000 (1800 actually) the warning disapears. It does not happen when the car is ideling in first and I am stopped or when the car is in park. The engine sounds fine and everything seems to run smoothly. The downshift is a little jerky from 2nd to 1st but I thought that was normal for VWs. Otherwise, like I said, this car is pristine. The oil level is fine and was just changed. Any idea what's going on or how I should start fixing?

5w-30 or 5w-20 fully synthetic?

I'm not sure what is in there now...It just looks like it has just been changed. I was going to try changing the oil and putting in a 5w 40 synthetic. What do you suggest?

I suggest putting exactly what VW says. Syntetic is a little expensive, but the oil changes are farther out too i.e. 5k-7k. Also, 5w40 is thicker than 5w30 or 5w20.

Also, check if t-belt was changed, pricy job (one hint, is that it might say on the belt itself).

Good luck,

Thanks for the replies and suggestions. I had the oil changed this morning. Now it has 10w 30 fully synthetic. That did not resolve the problem. What are the chances that it is a bad oil pressure sensor given the fact that it happens so predictably at certain RPMs?
Also, I am reading and reading about VW owners saying that they too were having issues with the oil pressure warning. Most of them ended with the engine being shot due to engine sludge. Most of them also state that they have a 1.8 Passat. Do you think that I should be concerned about the oil sludge and engine issues they seemed to have? My Passat is an '01 V6 GLS with 145k mi and you can barely hear the engine run...Am I a likely sludge candidate?

May have a bad oil pump or cam adjusters. I have never replaced an oil pressure sensor on a V6 but I do know its a common problem on 2.0L and 1.8t