OP update:
Received a new Jetpack and have been using it without incident. Data usage is now what I consider normal for me. Now I will say I am watching like a hawk and shutting down programs so they can't run in the background any longer and have auto-updates turned off for Windows. I was NOT seeing the normal installation message on shutdown and do not believe this caused my three huge spikes. I firmly believe that the previous MiFi was faulting. It always worked kind of weird from the get-go over a eyar ago but the huge spikes were new.
Verizon techs were pleasant and tried but did little to resolve this issue until the third call. I opted to get a new Jetpack as I was desperate to get back online for work! The local library was not a good option........
THANKS to all for your thoughts here. I will refer back and try some of the final "fixes" if I see spikes again. Hopefully this is finished and behind me!!