Took a short drive, and within minutes the clutch pedal stuck to the floor 3 times. I can bring it back up with my foot and there's decent pressure in the lines, but it's only a matter of shifts before it's stuck again. Both cylinders and the clutch were replaced about 10k ago, and I haven't had this issue before. What could be the culprit?

Clutch slave cylinder its mounted right in front of the tranny. Held in by 2 bolts. Check to see if you see any wet spots. Sounds like theres air in the system. Try bleeding it.

Chewing gum on the floor?

I don't chew gum, so no lol

When I picked the car up from the ****hole shop that did the clutch job, there was no pressure at all in the lines and I had a really hard time bleeding it. So I left it alone. Pressure built up as I drove it and it's been fine ever since, til today. I'm wondering if the air has been working its way through the system this whole time.

Unlikely, if you had any air the pedal would have been soft the whole time.

Is the reservoir full?

Yes.

I just finished replacing the lines with a SS braided one piece clutch line. It didn't solve my problem, unfortunately. There were no leaks evident at either cylinder.

When I changed to a SS braided line, I had real round trying to get all of the air out of the system. The clutch pedal would stick to the floor. I finally hooked up an oil extractor (pictured below) using a clear plastic tube to the bleeder nipple and used it to evacuate the system.

One trick that I had to figure out was to use some yellow gas line teflon tape to seal the bleeder valve threads. Air was entering the system through the bleeder valve threads whenever I would open the valve.

You can see a few air bubbles leaving the system in the 3rd picture below.

Hi, popo check the seal or gasket that the cylinder sits on.

Tried a pump. Ended up breaking it. Used the hose between a cup with brake fluid in it and the slave bleeder. Now the slave doesn't move at all and the pedal sinks to the floor with the slightest pressure on it.

Installed a new slave, just in case. Bled the line. Not a single air bubble came out. For over half an hour all we got was fluid coming out of the bleeder. Took the car for a test drive. The pedal is still sticking when shifting into 1st and 2nd gear. All the other gears seem unaffected by this. I'm stumped as to why this is happening.

man, and they say auto is for the birds, ha!!! gl with that, sounds like a pita.