alright so i recently got back from school in NC and am now home in MD and with my truck once again

. so i get back and soon find out that my battery stays dead even after jumpstarting the truck. basically i would jumpstart it, run it for about 20-30 minutes and then park it and it wouldnt restart after running for that long, it was completely dead. so i asked around and decided to buy a new battery. i drove to sears and bought a new die hard battery, installed it and the thing ran like a champ for the past week and a half until today...i went to start it this morning and it seemed like it had a weak charge and then drove it a little bit, parked, and then went to restart it and it had a little bit of juice left, but not enough to start it. so im thinking its the alternator now so im basically trying to figure out what you guys think about the problem, and if i need a new alternator which brands/types to look at. thanks.