2003 Tahoe Oil Gauge is whacky !

On a long drive last month  (200+ miles) the oil pressure gauge dropped but in  a strange way.  The needle shifted position so that when idle it went way below zero and when giving gas it came up to around 20 (instead of 40 or more) But engone sounded fine..   After two days it reset itself and worked correctly until the next big drive.  This time the needle shifted the other way.   It acted like 40 was Zero and went way off the charts on the high end when I gave it gas.  I brough the truck into the local dealer 2 days ago.  Of course on the way there the gauge went back to normal.  The dealer says the pump would cause the problem and wants $850 to replace it.  I don't think the pump is bad (dealer said it is pumping fine).  Engine sounds great.. I think maybe just a sending unit but dealer said no.  Anyone have any suggestions or experience with this problem ??
 
Thanks.
 
 

Either the gauge is faulty or the oil pressure sending unit is shot.

If it were a bad oil pump you would know it in short order......you would instantly become a pedestrian. 
  My best guess is it’s a faulty gauge, very common problem on the 2003 product and also very easy to repair, it requires a new gauge stepper motor that sell for about $10, replace them all (6) while you’re in there.

Thanks for the info.. I didn't think it was the pump either. Picked it up last night and it drives fine.  Chevy dealer just trying to get $850 I guess...
 
I'll change the motors!
 
Thanks again.