Jason is right on the money IMO. The problem with some new temp senders is the resistance is to low which allows the temp gage to register to much needle travel.
Even the newer AC Delco ones are NFG. There are some charts that compare the static resistance, and I will see if I can find it. However you may try and find a servicable OE one or go with the one from Lectric Limited.
Temp Senders
Ohm Chart
Mike