Here's a nifty little tool I've come across. It works for your adventures on Haleakala as well as the Road to Hana.
You'll download the app while you have a wifi connection, and it will work even when you lose your cell
signal (as you will in spots of both of these tours).
I used this app on recent drive on the Hana Highway. I found it to be very informative and interesting. It told me a few things, even I did not know. Some will find the delivery a bit campy. But, it tries to be as "Hawaiian" as possible to create an atmosphere to match your surroundings as you drive. There are recordings for each tidbit of info which get triggered as you reach certain points on the map, using your phone's GPS. I found the recordings to be well spaced and far enough ahead of the areas to give you time to decide if you wanted to make that stop. I think it's a real winner and a must have, ESPECIALLY if it's your first trip to Maui. Click on these links for iPhone and Android.