Help with 2007 Tahoe remote programming

[SCSassy]

I recently purchased a used 2007 Tahoe LT and I'm having trouble with programming new remotes to my vehicle. The Tahoe came with one remote and one key that work beautifully, but of course I needed spares so I purchased a used gm remote (for the internal components) and a new, empty pink remote. When I received the remotes I swapped the internal components into the pink case and followed the instructions for relearning the remote and it programmed immediately. It worked fine for 4 days, then it just stopped. I used it to drive my kids to school and an hour later it wouldn't work when I tried to go out again. The funny thing was, the original remote wouldn't work either, so I set out to reprogram them both and the original works fine, but the pink one will not reprogram. I changed the batteries so that isn't the problem. Do I have to take it to the dealer to have the remote programmed? The manual says I can have a maximum of eight transmitters, but I can't seem to get 2 to work at the same time. Is it possible other transmitters from the previous owner are still stored in my computer and not being flushed out when I reprogram the new remote?