maybe you banged your air flow meter around to much, have you got an after marker air filter,if so check that when you put it on you didnt damamge the afm, but it sound like you might have an electriacl problem in your car if it dies on the freeway, get it checked out by a proffesional they should be able to find out if you havnt got a good earth to your fuel pump and so on,. good luck