If anyone is having a hard time with the stunt jumps, you should check out
this helpful video
I just got done with them the other day. A few of them took a few tries. Quick saving before a jump helped.
I rage quit on the lighthouse one after wrecking about 20 cars. I'm doing the stunt jumps online though because they give RP. Hopefully they still count toward the achievement.
i gave up on them becuase on the last two i had left i went to do it and when i landed it said "undefined" and it didn't count it and now everytime i do one thats what it says
^I had two left and they said undefined as well. Probably because I had attempted them before but failed them or they were already completed. Perhaps the ones you're missing are elsewhere.
thats the thing though i have the brady games book so i know i did them all in order but the last 2 won't register for me
Try doing it with a different character. It is a bit glitchy. And I do recall the last two I needed saying undefined.