Sounds like you have a short list of things to get resolved?
(1) Crawler Box
(2) Drivetrain Vibration
(3) Speed Sensor
I have no doubt that you'll get it rock solid soon! ![Driving :driving:](https://board.marlincrawler.com/Smileys/marlin/driving.gif)
Not sure that I have a crawl box problem anymore. I think it is purely drive line. When I throw yours in though that will tell me.