From Syosset onward, I always use the following route:
- Woodbury Road to Pulaski Rd. 13 miles to Rt. 25A in Kings Park.
- Make right, 2 miles to fork, straight onto ROSE STREET
- To LANDING AVENUE. Make RIGHT
- 2 miles to EDGEWOOD in Smithtown. Make LEFT
- 2 miles to 25A
- 4 miles to fork in Stony Brook. Bear left
- ½ mile to fork. Bear RIGHT and stay on 25A
- 5.75 miles, pass Setauket, to ferry
I didn't get to check your map closely, but it appeared you were using 25A a lot of the way. Pulaski Rd is much quieter and flatter.