My 2003 Chevy Trailblazer Ext with the inline 6 cylinder engine with 171,000 miles has suddenly started to loose oil pressure at idle. After normal operation for a period of time, when I slow down to a lower RPM or come a stop, the oil pressure drops to almost nothing and the stop engine soon message appears. It has a fresh oil change and has a new sending unit. The idle RPM is generally around 600 - 700. If I increase the RPM slightly it will hold normal oil pressure. I have a friend who has a 2004 GMC envoy which is doing the same thing. Has anyone experienced this problem, if so what has been discovered that could solve this problem? Any help would be appreciated. Thanks

Is it making any bad noises?

First change out the oil pressure sensor if you don't know of it being changed in the last couple thousand miles.

There is no abnormal sound from the engine. even when it shutdown, it will start up again. The first things that I have done was to do a complete oil change with the manufacturers recommended oil and filter. Also, the oil pressure sensor on the oil filter housing has been changed.

Like after I suggested it or it was done already?