1999 Dodge Cummins clutch

An inch or so of free play is normal in all clutches so there is not any force applied to the throw out bearing between shifts. That's why they say to not "ride the clutch" when not shifting.

It's more than an inch of play

You would bleed the master cylinder when the pedal is spongy, just like brakes. Make sure your fluid level is up. If there is too much free play, it will have to be adjusted and I am not familiar with this type. On a semi we would reach through a hole at the bottom of the bell housing with an extension and turn the adjuster while someone in the cab would feel for some free play. What's happening is you gain free play as the clutch wears, but there is plenty of clutch material to adjust them several times. Semis go 300,000 miles an a clutch and a 13 speed Road Ranger tranny. Your truck probably has a ceramic clutch too.