I have a really old MinKota trolling motor that went too fast. I put a little PWM (Power Wave Modulation) unit in line with my trolling motor. I can dial in any speed I want. Very energy efficient with no energy lost in heat generation. Cost $18.00 from China. Found it on Amazon. Installed it this spring, but have probably used it 15-20 times. Sure made my fishing a lot more enjoyable.