I take my Roxor on state highways (e.g. 60, 89, etc). Interstates are a no go - illegal in AZ (and probably any other state).
Well, funny you ask about freeways. One time last year, I drove about 30 miles on I-40 in northern Arizona between Williams and Ash Fork. There are only dirt roads, which would have doubled the miles and time. So, I chanced it. At 7000 ft altitude and a decent multi-mile climb, the Stage 2 got me up to 55 mph. I hoped to not get caught on a freeway. Semis and cars flew past me. Not something I need to repeat any time soon.
Good luck with your decision on the ECU.