Chris;

If simply moving the needle manually past the sticky point and exercising it a few times cleared it, be happy it was a simple fix (how long it will last is another question) ...it still does sound to me like a mechanical issues...it could have been something as simple as a piece of dust or debris had gotten into the pivot enough to bind it up from going past the 1500 mark...it wouldn't take much...were talking about a very fine mechanism (watchmaker stuff!) here...

I can't help with a sensor, but I recall Temp vs Resistance charts for sensors in the factory green manuals...maybe you could start looking here: http://www.volvoamazonpictures.se/documents/Volvo_Amazon_manuals_en.php

Good Hunting!