davethehiker, next time you are getting ready for a range trip, try this:
Disassemble your Glock, grab just the barrel (make sure it is clean and dry inside), grab the ammo you want to use at the range, point the barrel straight down at the floor, and drop each single round into the chamber, then turn the barrel over (muzzle up) and let the round slide back out into your hand. Each round should make a metallic "Tink!" noise when it hits bottom in the chamber, and slide right back out when you turn the barrel over. If the round sounds different (no sound [indicates a dented round that may have wedged in the chamber], not a clear "Tink" sound, or makes a different sound) when it hits bottom, or doesn't slide right back out when you turn the barrel over to dump it out, set the round off to one side and don't use it on this trip; only use rounds that drop in all the way, and fall right back out.
When you are ready to reassemble your pistol, make sure it is lightly lubricated in accordance with the Glock manual instructions.
See if "sorting" your ammo before the trip, as described above, makes any difference in the reliability of your pistol.
If it does, you may want to try buying/using some different ammo.