The way I shifed the 2 speed in my truck(it was electric,but I'm sure the same method would apply) was,accelerate,upshift the 2 speed and let the throttle up,when you feel it shift,accelerate, shift the trans up,shift the 2 speed down,give it a dab of throttle,when you hear the axle shift accelerate,repeat step #1,accelerate,repeat #2 etc.you'll have to mess with it and get your timing right,it just takes some practice. as long as you do things a little gently until you sort it out,I doubt you'll do any damage to it. Get your brakes worked over,take it out and have some fun with it.
