When I have time I'll remove the radio so I can get at the main connector for the dash so I can inspect the pin for the temp gauge and check continuity to the sensor connector.

I wouldn't be surprised if there is a problem with the board on the back of the cluster. I replaced the board about 3 years ago when I had the column out for the power steering conversion. I replaced it because the connection to the right turn signal indicator was broken.

If I have to replace the board again this time is will be a brand new one.
https://www.ebay.com/itm/Mopar-Standard-Dash-Cluster-CIRCUIT-BOARD-71-74-B-Body-NEW-PDD-051/332494993093?hash=item4d6a3ef6c5%3Ag%3A4rIAAOSwyYFaO-Dg%3Asc%3AUSPSPriority%2154911%21US%21-1&_sacat=0&_nkw=mopar+b+body+gauge+cluster&_from=R40&rt=nc&_trksid=p2334524.m570.l1312.R2.TR0.TRC0.A0.H0.Xmopar+b+body+g.TRS2&LH_TitleDesc=0%7C0