Hi, I am getting older by minute so here goes. I have a Dodge Ram 50 (Mitsubishi), Awesome vehicle. Inexpensive , tough as nails, breaks down - limps home. I bought it new in 1992.It is manual transmission , cable actuated. New clutch and cable. my pedal is becoming non functional. My clutch cable is extended all the way out and has spacers on it to help the clutch engage.This is not a sudden , new, problem. It has progressed. Several months back I began to hear the under dash assembly squeak when I pushed on the pedal, but, I was sick and had to have surgery, so, wasn’t able to pursue the problem aggressively.I feel like there is a spring under the dash that has broken, worn, lost proper adjustment. I don’t know ,and, spec. illustrations do not show a spring, but , the sound I heard was the complaint of a spring. If this is amusing , I have more comedy to come. I also have a 1973 Opel Gt and a 1987 Trans Am.
That clutch cable has to be anchored to the firewall. I would take a close look at that area to see if after 26 years that area is flexing or cracked, allowing the cable to move and not operate the clutch properly.
After checking the firewall for cracks, listen under the truck while someone pushes the clutch pedal. The pressure plate spring itself may have broken. I’ve had this happen and the clutch pedal just goes away much like you describe.
Amusing ? Comedy ? 
Thank you, I found no damage to tube or area around firewall. My clutch is
fairly new and works well. I added a 1/2" rubber bushing to the shims I
already have on my clutch cable, and, I have a normal cutch again. A
mechanic who worked on my truck came up with the idea of bushing the clutch
cable further away from the firewall because I could not get enough
adjustment. He said that would help for now, but, he did not know what was
wrong.
I found a diagram of my clutch lever where it enters into the side of the
transmission. On it are two springs , a return spring and a release spring.
I think they are worn out. No one carries them , but, I found them on
Amazon for $8.00.
I am considering this seriously because my truck has not failed. It has
fallen out of adjustment and responds to being brought back into
adjustment. That makes me think I am dealing with a worn part as opposed to
a broken part. This truck is a much better vehicle than I am mechanic. So,
I often struggle to resolve an issue and then I have to laugh at how simple
it was. Thank you and I will let you know if what I think is wrong has any
merit.
When you replaced the clutch did you replace the throw-out bearing and the clip that holds it in place? Something is wearing out or slipping, making you have to move the clutch pedal more to rotate the shaft that operates to release the clutch. It could be the cable stretching, or either end of the cable housing breaking down, the pivot point on the clutch pedal linkage wearing out, the lever on the release shaft slipping, the bushing the shaft goes through wearing out. Any of those things can cause this sort of behavior.
I didn’t replace the clutch . I had the local high school automotive
teacher do it. He was previously an engineer at FOMOCO. My clutch worked
and works fine. He told me my clutch was not as worn out as I though it was
, and, He inspected it and told me other things that needed to be replaced.
So, I had them replaced them while the clutch was being replaced. My new
Clutch cables work the same as my old ones . Right now I have three that
are the same length. At 285,000 miles I realize I am in mostly uncharted
territory. But, this did not happen suddenly, I have felt it coming on for
some time , and , now that the problem it is more obvious to me. I feel
reasonably sure that it is not the clutch. I have visually and by hand
checked my clutch pedal assembly and firewall housing finding no cracks
damage or unusual wear. My suspicion is now on the clutch lever going into
the transmission and its associated springs.