96 pathfinder clutch pedal has lost pressure,

Can you see the clutch slave cyl?
Is it extended fully?
Is this condition after you bled the system?
Try opening the bleeder on the slave cyl in case you have full pressure in the system right now.Also make sure the new master cyl rod from the clutch pedal allows the master cyl to return fully to it's retracted position or the pressure will build up an lock the pedal as yours is.
You want a little play in the clutch pedal rod to master cyl.

Master or slave cylinder blew out. Could be the pressure line also.

clutch pedals are suposed to go all the way to the floor , you sure you dont mean brake pedal (cus thats bad ! ) clutches should travel all the way to floor and release the "grab" of the engine about 2/3 down , this way they are more smoothly allowing shifting thru the gears and not jerking as you shift thru the gears , if clutch pedal does not start to "grab" the engines power by 2/3 off the floor and fully "grab"its power all the way up(slipping) ,and you have a hydraulic clutch (96's do) then the clutch disk may require replacement or there is a oil leak in the clutch/master/slave cylinder , look for small oil leaks from under car in area of foot pedals
clutches should be replaced as an assembly that includes , disk ,pressure plate, throwout bearing , with engine side clutch plate magnafluxed for heat cracks and any hydraulic oil leaks replaced or repaired

The clutch don't have spring to return. hydraulic pressure return the pedal. if you pedal go down to the flour and don't return you lost the pressure. First look in the reservoir for fluid. add DOT3 brake fluid and bleed the system. inspect for leak
Good luck

Replace the Clutch Master & Slave Assy

lubricate clutch pedal at pivot points

Check the clutch pedal return spring, which could be broken.

It's time for new clutch set for your car. Good practice to always change the parts for clutch system. Clutch, pressure plate, throw out bearing.

THe problem can only really be with the clutch master cylinder. What you describe sounds like the master cylinder is not relieving pressure and this is building up in the salve cylinder, applying pressure to the pressure place and causing the clutch to slip. Can you make the problem go away even temporarily, if you open the bleed screw on the slave cylinder? You say that the free play is correct, but is the master cylinder returning fully to its released position?

Stop driving the car now! The clutch master cylinder has an adjustable pushrod, it is set up too long now. Take it back to where it was done and tell them if they don't know how to set up clutch free play, they shouldn't have attempted the job. This may have cost you a $3500. clutch job. Get it adjusted fast.