Jim did you find any answers elsewhere? I have a similar problem--oversized furnace that's been bouncing off the high limit since bought 20 years ago. Fat stack of work orders and no fix. I've asked in other forums about "turning it down" and have been told IF you can find someone cavalier enough to try, you can only safely reduce output about 10%.
I was a little shocked that although this IS a common problem nobody has invented some solution. I would have thought with such a ready market some eager manufacturer would have invented a modulating gas valve that could be retrofit into older furnaces. Either I don't understand the complexities (they're common in industrial environments) or the perceived liability is too great.
For myself, this winter has been too frustrating to allow my furnace to continue to run in such an inefficient manner so I replaced the 220 limit with a 240 and it's happily purring along now. I'll start saving my coins til I can afford to replace my perfectly-healthy oversized furnace with a new unit...from an honest company.