inacurate temp. guage

[popsthebuilder]

73 c20 350 th350
 Checked old posts and couldn't find anything on my specific problem.
My temperature gauge kinda sorta works. When engine warms up the gauge barely moves from its' resting spot. when I get on the interstate for a while the gauge reads 1/4 of the way to hot. Sometimes when I kill the truck the gauge will peg out and if I turn the key to on then it will settle back to its normal inaccurate reading. She can't be running that cool. The is definitely exhibiting strange behavior. Any thoughts on were to start to troubleshoot. I guess it's probably time to purchase a multimeter and learn how to use it. 
Any suggestions are greatly appreciated as always.

[bake74]

     Read the post in the tech section by bd on troubleshooting gauges, then find out if your sending unit is bad.  Which might be the case.
     Knowing how to use a multi meter and test light is knowledge that will go a very long way with these trucks.  I would do my research and homework and get to know how to use both.  Once you understand the basic's you can go from there.
     I will add 1 thing, the cheapest multimeter out there is not the best buy.  You need one that at bare minimum reads D/C volts, ohms, and continuity.  I would opt for one that does a/c volts and amps also, so you can use it for other things.

[popsthebuilder]

Helpful, as usual. Thanks Bake74.