This is a similar problem with the Pontiacs: all the aftermarket senders are essentially calibrated for the idiot lights even though they sell them to fit the cars with gauges. So they read waaaaaay high. I am currently hunting for the right sender for my T/A which at the moment reads 210 when it is actually 170 (checked with an actual thermometer).
Read here:
http://forums.performanceyears.com/f...d.php?t=632070
This company supposedly sells a correct sender:
http://www.lectriclimited.com/mainpage.htm