rpm issues

After warming up my truck this morning I noticed that my truck was idling at 2700 rpms. While driving my truck the rpms were over 4000. when I got to work and shut my truck off the guage read 2000 and stayed there even though the truck was completely off. Can someone please help me with this?

P.S. 2004 Chevy trailblazer 4wd 6 Cylinder

Welcome to AF, can we assume the engine was really not idling at 2700?, if so the usual problem is the tach stepper motor which requires removing the cluster and disassembling the tach.

Thanks for the help. I should get some time to work on this issue soon.