Temp Gauge swings toward high-side and back to norm with 3 sec
I would think if the IVR was failing the fuel gauge would act up as well.
I would try another sender, and most you guys know I don't like "throwing parts" at a problem. If that doesn't fix it, wiring problem, bad gauge unit itself
See if you can see the fuel gauge act up.........at all......it's the IVR