Arggh! I've tried to find exact pictures of this layout in whole given that pics help. Being there would be and just might be necessary to know exactly why this is like this and could be like that for so long as I would have guessed a failure would have happened by how I am interpreting your situation.
Seems universal that this is not adjustable. That alone doesn't mean things are all fine or will behave fine with engagement and disengagement at the right spot in the travel of the pedal inside. It should have some "free-play" area at the top such that you could just push it with your finger and have some "nothing" room which is needed. I'm not sure our understanding of what you are describing and how we are interpreting just what it's doing and that happens. The web is fantastic but not like experience and actually seeing and touching things whatever they are.
Found that the fork that the slave cylinder seems to be a popular replacement item for this. Not sure how much of this part you can see if much at all but it's like this.......
The slave cylinder has a fixed rod that pushes on the lower left of that bar if you will with the dimple centering the pushrod of the slave which looks like this....
That pointed rod is at a set length so would not be adjustable as said. If there was no air, no fault in the hydraulics anywhere, not a bend pedal inside or floor somehow bent up in the travel area IMO there is a higher chance that this item or the fork has an issue. I'm plain not sure you can view it operating in this case.
Some of these set up the bleeding is VERY difficult to get right. So if in the life it needed to be bled it could still have air which IMO and experience would make the actual pressure to release, disengage clutch where it would also engage be lower to the floor. Air would highly likely be odd feeling at assorted temps or multiple pushes on clutch pedal may change it's spot where on pedal travel the show happens.
Trouble is to fully investigate this hands on you or a tech would first check that the pedal and pivot action inside was fine, might plug master cylinder with line removed to feel then a solid hard pedal, watch the action at the slave and just might have to remove the transmission to check it out more if it can't be seen or an inspection cover removed. That fork probably requires transmission removal if bent, worn somehow. If that and keeping this almost anyone would suggest doing a full clutch replacement job. If not a rusted mess it may not be that horrible to do labor/time wise.
I'm reading between the lines that you care about this truck enough to replace the rubber floor/carpet, have just said you don't put that many miles on it. Hey, having this vehicle is probably very useful. Being a GM truck especially there will be parts for it for ages including many common things that would be dealer only.
In short this isn't the way the clutch should behave. I/we can't know your abilities to rule everything out down to the last possible reason for this or if you really are willing to pay to take it apart down to the clutch or do that yourself. I didn't check but I wouldn't have it all apart and not put a new clutch job with parts generally not that costly as things go vs time to get there. By age alone if keeping it, it would be nice to know it was done but just a clutch job alone isn't necessarily going to change this problem so it needs to be checked while intact now IMO by you or a tech.
If nothing else I'll warn you that if there's a hole in the rubber flooring it will get moisture in there that will not dry out well and be another problem entirely to fix. Such is life,
T
