Will 15 inch wheels fit a 1999 gmc sierra z71?

SOURCE: gmc sierra z71 rotor problem

sounds like you have a worn wheel bearing which is replaced as a hub assembly the rotor just sits on the hub and wheel hold rotor tight

SOURCE: low oil pressure

It is a plu located directly above your filter on the oil filter adapter housing.. its about 3 inches long with wires plugged into it.. takes a special little socket to remove it...10 dollars at auto stores for the socket...

SOURCE: putting 19 inch 2007 porsche 911 turbo wheels on 2001 like car

CHECK WITH DEALERS BECAUSE WHEELS ARE DIFFERENT WIDTHS AND NORMAL CAN NOT ALTERED OR MOVED FROM FRONT TO
THIS IS A DESIGN FEATURE

SOURCE: gmc sierra 2008 low tire pressure problem

You can follow this to reset it.
Ignition ON, initiate the TPM Learn Mode
using one of the following procedures:

1. On vehicles equipped with keyless entry, simultaneously press the keyless entry transmitters lock and unlock buttons until a double horn chirp sounds indicating the Learn Mode has been enabled. The left front turn signal will also be illuminated.
   
2. On vehicles not equipped with keyless entry, press and release the driver information center (DIC) INFO button until the TIRE LEARN message appears on the DIC display. Press and hold the SET/RESET button until a double horn chirp sounds indicating the Learn Mode has been enabled. The left front turn signal will also be illuminated.
3. Increase/decrease the tire pressure for 8-10 seconds then wait for a horn chirp. The horn chirp may occur before or up to 30 seconds after the 8-10 second pressure increase/decrease time period has been reached. Once the horn chirp has sounded, the sensor information is learned and the turn signal in the next location to be learned will illuminate.
   After the horn chirp has sounded and the right front turn signal is illuminated, repeat step 2 for the remaining 3 sensors in the following order:
   3.1. Right front
   
   3.2. Right rear
   
   3.3. Left rear
   
   When the left rear sensor has been learned and a double horn chirp has sounded, the learn process is complete and the RCDLR exits the learn mode.
   Ignition OFF, adjust all tires to the recommended pressures

SOURCE: 1999 gmc sierra rear brake trouble

Most likely a the caliper needs to be replaced. Could be more than that though, maybe brake hose. open brake bleeder and make sure you are getting brake fluid from the hose.