My tachometer on my 2003 Tahoe z71 142k miles recently started acting up. Sometimes it was fine, sometimes it was working but very inaccurate, and sometimes not working at all. I pulled the cluster out to check the solder on the pins where the connector is and they were all perfect so I didn't touch them. I noticed another area on the board with some heat discoloration around resistors that wasn't there when I reflowed the resistors for the PRNDL indicator not working. I reflowed the solder on those 3 resistors and my tachometer again works perfectly. Lots of info out there on the PRNDL but I've never seen anything on the Tach other than the stepper motor is bad. Here is the location of the Tach resistors. In hindsight, while I had it out I should have reflowed all surface mount resistors as preventive maintenance. Another tip is before you pull the needles off the gauges to remove the board, put small pieces of painters tape under all the needles rotated as far counterclockwise as they go and mark position. When putting them back on, just have them on enough for a small amount of friction and rotate them counterclockwise to the marked position to keep them reading correctly before pressing them on tight.