Why do my remote key-less entries on my 2005 GMC truck with new batteries lock my doors but will not unlock them?

I had the reverse problem not long after the remote took a swim in the ocean... but turns out that the ocean had nothing to do with it - it is sealed pretty well! I took it apart to see what battery it took, but shile there, cleaned the contact surfaces CAREFULLY (they looked to have some debris/wear from use, its a 2003), and reassembled - fixed it. I thought the battery was At Fault first too, but i never made it as far as getting the battery.... that said, there may be a function that you can hit the buttons in some order to disable or enable parts of the functions, that is not something I have fooled around with... -KS