The RL does not have a 2 speed gearbox. Do you air down in the sand? If so, and you go low enough to turn on the TPMS light, you cannot disable VSA with the cabin switch. (VSA is your traction control and when it can't control wheelspin with brakes, it will cut the throttle making it feel like you're bogging down in sand, snow, mud, etc.).
Whenever you need wheelspin to maintain momentum, always turn off VSA. If you're aired down for the sand and the TPMS light is on, you'll have to pull the 20A VSA fuse in the underhood fusebox in order to kill VSA. (safety feature) Remember to replace the fuse when you get back on the road. With all the lights on your panel, you shouldn't forget!
The VTM-4 button is a manual backup to the automatic 4wd system and only works in 1,2 or R. While the automatic 4wd system is phased in depending on certain factors, the manual system provides maximum 4wd at once and begins to phase out above 6mph until it's totally off at 18 mph. It will re-engage automatically when your speed drops below 18 mph per the above.
BTW, if you select gear position 2, you are always in 2. It does not start out in 1 and then shift to 2. So you can easily overheat the tranny fluid if you use this. Just be advised.