Yes, those directions exactly except it takes more like 1 1/2 hours for the entire trip. The sign off the main highway for Jarabacoa is small so be on the lookout for it. Like windeguy said, you turn right off the highway there and then go left under the highway and then straight at the light (gas station on right) and then up the mountain. To get to the main highway going out of Santo Domingo (called autopiso Duarte), simply get on John F Kennedy and take it north. Avoid doing this during rush hour or it may take a while to get out of the city.
Larry