I spent weeks tracking down the culprit to an instrument cluster issue and engine check light malfunction. This went way beyond a common speedo recalibration issue. The gauges would just stop working periodically. Although you don't hear a lot of about it, reoccurring instrument cluster issues like what I experienced are often the hardest to diagnose because there can be so many variables as to what is causing the problem.
Whether your cluster is analog or digital, faulty circuit boards to broken solider joints or wiring is often at the heart of the problem. Like passenger cars, RV instrument clusters fail and unfortunately there doesn't seem to be a lot places to turn when something does happen. This is especially true with older motorhomes.
After my problem began, I immediately started searching the web for places that could solve it, but after weeks of research I came up empty handed. The local dealership couldn't figure it out either! So I was stuck, until I discovered a business that specializes in speedometer and instrument cluster repair work, including ABS modules and HVAC repair.
I don't usually recommend mechanics or technicians, because people can have different experiences, but Digital Auto Technology (DAT) did what they promised and got the entire instrument cluster working in short order and it was very affordable (about $150).
Once I removed the digital cluster from the dash I dropped it off to DAT and in 24 hours my problem was solved, even though many others couldn't even diagnose the cluster. DAT often ends up replacing most of the components instead of just doing a quick fix, but whatever they did, it worked and I recommend giving them a call if by chance you or someone you know is experiencing speedometer issues of any kind. They can be reached at http://www.digitalautotech.com.
Hopefully, this recommendation will save you some research time. Let me know how it goes.