Also, there are different temperature range senders and gauges. The sender has to match the gauge or the readings will be off. Is it possible that the original sender or gauge was bad and you got a mismatched set when fixing it?
Coincidentally, we are having the same problem, but I have isolated it to the gauge itself (a benefit of having a "spare" engine onboard - troubleshooting is quicker).
You do not need a parachute to skydive. You only need a parachute to skydive twice.