Ok! Here's the story. This past Summer, i had started having trouble starting my 03 Tahoe. All i would get when trying to start it were clicks. I took my battery to Autozone to get it checked out. They said my battery was fine. At first I thought it was having trouble starting because of the high temperatures. Well a couple of months passed and i started having the same problems. i then decided to go to a local gmc dealership and purchased a alternator for $450 installed, thinking the battery wasn't getting a good charge because of a bad alternator. after about only a week, the same problem occured. i was hot. I then went back to autozone to purchase a red top altima battery. it was running fine for a few months and now today. i go to start my tahoe in the cold and "click, click, click, click". talk about anger! what should i do?? should i go get a new starter?> keep in mind, i have already taken it to bill heard chevrolet (the dealership i purchased my vehicle) and said they couldn't do anything for me. any places online where i should purchase a starter if i should get one?

any help would be greatly appreciated