It's still under warranty - I'd certainly be back in touch with the seller about how it's dying on you.
No problem at those speeds. Maintaining 70+ can be in issue if significant headwinds, grades, etc.
/moved to marketplace
May need to come all the way down to 1st. Are you bogging out in 1st, or the higher gears?
Sounds like a good choice!
Found some info here, no personal experience with these folks:
Separate names with a comma.