Check your ground wire on the gauge. Even thou you are using the line and it should be grounded, maybe it's not enough? I tapped into the rubber hose part of the line, so I had to add a separate ground wire to the sendor. I didn't do that at first, and wondered why my gauge did not move....
If the grounds are ok, you should have seen it at least move some when you got into stop and go traffic. Try backing up an incline, like a drive way, and you should see the needle move....
Mine will run just above the 100* mark while on the hwy in winter. Summer, it'll go to 150* and towing it'll go to 180*.
When the TC unlocks, you should see it rise as well. Then, when it locks, you sould see it drop some.
Good luck!
Mitch