Bill on any dash containing temp, fuel, and on Ralleye, oil pressure, if one works properly, then the IVR is at least working.
Some other causes depending on the dash TYPE, meaning more than one PC board, Ralleye, year, etc........
1....Bad connections at the gauge stud nuts. Loosen / tighten them a few times to "scrub" the contact and nut clean. Consider replacing with "real" nuts
2...Loose / broken board connector pins or bad connection in the cluster connector
3....A bad gauge, but I thought I saw the other day you grounded the sender and the gauge went over to the pin? This would indicate that the gauge may or may not be accurate, but at least "works." But "it might be" that something is intermittent in the gauge, debri, sticking, corrosion, etc, that is preventing it moving, or even an intermittent electrical problem
4....Bad/ poor conneciton in the bulkhead connector
5....Bad/poor connection in the connector right at the sender. These can break internally in the molded plastic, and appear OK
6...Bad/ intermittent sender, but I guess? you tried another?
GROUND.....You really should add a ground pigtail from the cluster to either the dash frame or the column support bracket