I got an 01 s-10. When i put my truck in reverse my gauge will either go up or down. then when i put it into drive it will move up or down and it will stay until i take it out of drive. But then when i put it into park same thing the needle will go up or down so at times i really do not know if i need gas or not.

That's weird fireonlock!

Just a guess, but look to see if your shift linkage is touching any wires. It might be tugging the wire a bit.

You should only have to look under the hood, and under the truck. Not under the dash.