Yours still sounds like master going bad, and depending on mileage changing the master doesn't hurt anything. Pain in the rear and wallet maybe, but it is 27 yrs old and if it's original OEM, replacement even if found to not be the problem just ends up be predictive/preventative maintenance.
With current quality issues I have experience the past few years, i will not do a "rebuilt" Master cylinder, too many field failures. I only buy new, name brand if I can.
On the comment of locking the brakes, if the rears locked and front didn't, it could be an issue with the combination valve, but with the pedal going down that far before it starts braking, I would keep with the simple stuff first and still inclined to think its the master.
If yours has ABS It would need to be properly checked. Most systems back then were fairly simple, but ABS was still fairly new. You will need a tech or shop that knows that system.
Historical from factory known issues: there were 4 known major issues and one of these issues on the 92 W250/D250 was with the rear shoes on the 12 inch drums.
Problems/Dodge/Dodge W250/Revised rear brake shoes
Vehicles equipped with 12" diameter rear brakes may encounter premature rear brake shoe wear.
Revised brake shoes are available for this concern.
1990, 1991, 1992, 1993