When you say chugs along, do you mean it chugs then dies? Then you try it again? Also, when pulling onto a highway you're usually going at an angle i.e. turning, classic signs of a bad fuel pump (the car dying when taking a turn). Since you have a 99 it could be a dirty sock filter since I'm assuming you have a return system. Can you check to see if you have a return or returnless sytem? I may not be able to diagnose this, but giving out more info. about it will most likely help one of the gurus on here help you out.
(Just for yourinfo, post problems about the vehicle in the troubleshooting forum. People most likely won't help you since they will never see it, since this is in the wrong forum.) Anyways, good luck!
