im not familiar with sand at all, but if you are bogging 6th gear, your mains are probably rich
if im on loose shit, i will start in 2nd and just sit farther forward to get the tires spinning, then once movin and spinnin plop your ass back down as far back on the seat as possible, im sure the kind of tires and how many paddles you are running makes a big difference as well, but like i said ive never ridden sand