Since you have a 2005 your instruments are driven by an MMDC and not a VDC which was replaced in 2004 late model Winnebago's. That said, you might have a bad ground problem.
On attempt to fix it might be to add a ground wire to your Medallion instrument cluster, even though it's a shot in the dark it maybe a good starting point.
FYI, that air chuck up front is there for convenience, to run your air tools or bicycle pump, but it can leak. Or not? I spay mine with WD-40 and then some lubricating oil... but if it's leaking you would hear it or feel it. Do you hear any air leaking or can you feel any air leaking out?
Does your air suspension system work properly?
Do your other instrument gauges work properly?
I would look around your air dryer for leaks or a constant purging of air.
This is not my area of expertise, but if your suspension is normal I would think you have a gauge problem. This is why I suggest you start by adding a ground wire to your MMDC and if that does not work, hopefully someone else will chime in and point you in the right direction.
The MMDC works like my VDC only I hear it's located under your dash. (My VDC is located by the engine where there is more heat and vibration.) You should be able to identify your MMDC by tracing your red and green air lines under your dash. And I'm told the MMDC performs the same functions as the VDC so "cold solder joints" could be your problem.
This thread applies to pre 2004.5 Winnebago's with a VDC, but it may help you if your MMDC is also failing: