Just recently when temp gauge is up to temp 90 and car is warm the gauge sometimes drops to about 80 then slowy go's back to normal. Ive changed the sensor a while back to the green version could this be a thermostat problem? car runs fine should i be worried?

Dont worry about it. As you say it could be the thermostat.

Mine sometimes moves a little off 90, usually when I'm free wheeling for long periods. When the powers back on its fine.

Yeah funny that mine seems to do the same.