I suspect you have either a broken band or a broken servo shaft.
On the front band loosen the nut then see if you can torque the adjuster to 10 ft lb.
If the adjuster goes all the way in with out torqing to 10 ft lbs then the band is broke.
If it torques down ok then you will need to remove the servo and check the servo shaft.
You will also need to check the servo bore in the case if it is worn you will need to have a bore pin placed into it or case replaced.However with the mileage you have I would not suspect this.
The shaft is made to the servo and at the end of the shaft right at the servo are fluid holes in the servo pin. Here is a pick of one.
They will usually break at the fluid holes.
The other problem we see on this tranny that I was telling you about but we usually don't see this at the miles you have but is certainly a posibility is a worn servo bore.
Here is a pic of this.
What happens here is the piston wears a groove into the bore then it looses pressure around the shaft and can not apply the servo. If this is the case there is a repair out where you can drill out the bore and install a sleeve in it.
Yes it is the front one and I suspect with your mileage that it is a broken servo shaft. Have seen several of these. But it can also be the servo bore in which case the tranny would have to come out and be totally disassembled to repair this.
Of course if you pull the servo and the shaft is broken then you know you have found the problem. If the shaft is not broken then you would have to look into the bore and see if you have a groove worn in the bore.
If you do continue to drive it it will eventually burn up the band. If it is jerking while doing this it could possibly damage the center support.
You may have to use a magnet to get the other end out but thats it.Comes out easy usually.
You may also be able to drop the rear tranny mount and let the tranny drop down enough to get the servo out without taking the exhaust down. I can't remember on a 4.0.
Yeah I couldn't remember on the exhaust on a 4.0L. Working at a LM dealership we see mostly 4.6L and then the linc LS