rock crawling is all about a feather touch and slow going. These are two things that nitro are not best at. You are going to want the clutch to engage as early as possible before it builds up a lot of torque so you can have smooth and slow engagements. Gear up the ratio as much as possible. Put as tall of a spur gear and as small of a pinion as you can on your truck. Your engine is going to have to run very cool without any cooling airflow since crawling speeds are almost standstill. Also, a t-maxx cannot hold the torque on the drivetrain like an electric can. Electrics basically use a drag brake to keep the drivetrain from rolling free when you are sitting and planning your next move or line. As soon as you let off the gas, your t-maxx will roll backwards until you get the brake.

T-Maxxes are too big for any kind of standard crawling course.

So, frankly, I suggest you get a rock crawler or just do the best you can with what you have and not worry too much about it.