Q: My truck will not start at all!

Hello, well anyways I have a 2006 Chevy silverado. I had never had problems with it until I had problems with the transmission. It was driveable but when I would go over 30mph the rpm would go up and down by iteslf.I paid someone to check truck and they said it was transmission. They did the job replacing transmission but when they turned me in the truck ,the starter sounded weird when I would turn the truck on. It went away after a week. Then I got stranded I got it towèd to another mechanic and they said it was starter. I bought starter and they changed it out, but I also had to buy battery because they said battery was bad. Now, I drove for a couple of days and about to go to work in morning, and my truck did not start. Battery was low and even though it is new. I went to get it charged at auto zone a d put it back on truck and truck will not start so I disconnected battery and don't know what it next. Thank you!