Batteries are not rated to last much longer than what you've got out of it by now. That being said, my 97 battery is still going strong, and we just last week swapped out my son's original battery on the 94 Celica. Both Panasonics.
It could very well be your battery. You can take your truck/battery to many places to have it checked, but around my parts, they don't do this without charging you (and I'm cheap). If you can get it checked cheaply/quickly/easily, then do so. Otherwise, before I went replacing it, I'd do the following. Check:
1. That all cables/wires are firmly attached to the battery, with no corrosion. It wouldn't hurt to remove the battery terminals, clean, then reinstall, just to make sure.
2. That both ground strap and positive cable to the starter are clean with no corrosion. Again, cleaning and reinstalling would not be too difficult if you saw any signs of corrosion.
3. If #1 and #2 don't help, put a charger on it for a few hours, then try starting cold.
If #1 or #2 make it better, perhaps it was just some bad connections. If #3 makes it better, it could be your charging system; time to start checking that out (i.e., alternator not charging correctly). If none of those things work, then I'd look for a new battery.
Tom