Another option if you aren't in the market for a new trolling motor could be one of the old Minn Kota maximizer electronic power control units (if you can find one). Occasionally you can still find someone who has one for sale. They were an older option for achieving variable speed on a 5 speed. And GPS is key for measuring speed. If you don't have a GPS fish finder, just pick up a handheld GPS. They oftentimes update quicker anyway.