You need to make sure your clutch is being pressed far enough into release the pressure plate, but not too far, as it will bend the tabs and weaken the clutch. Measure your master cylinders piston diameter and the stock Dodge's. They should be the same, otherwise you will have problems.

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If the setup is not the same size, Wilwood offers some nice master cylinders (I am using one in my LS1 based engine Miata swap)

Without a method to bleed these system, I feel they are mediocre at best, and in reality..... junk.

Brake/hydraulic fluid attracts moisture..... Moisture lowers boiling points and is never good on anything

Update:
I looked under the dashboard and examined the rod the comes out of the clutch master cylinder and found that it was leaking fluid. So it is pretty obvious that this is what is causing the problem. To make things more confusing, the master cylinder is out of a 87-90 Jeep Wranger with a bore diameter of 11/16". The NV5600 slave cylinder is 7/8". It makes for a pretty light clutch feel.

Follow up:
The truck is fixed. :jump: I ordered and installed a new master cylinder from a 89 Wrangler. The truck was retrofitted to accept this master cylinder. The clutch pedal felt a little mushy at first but after about 3 days of short distance driving, it purged itself of all the air in the lines. The Jeep master cylinder has a smaller bore diameter (11/16") than the NV5600 slave cylinder (7/8") which makes a nice and light clutch pedal feel. Luckily, the Jeep master cylinder is long and has enough displacement to work with the larger piston slave cylinder. Anyways, this is good information for anyone who might be considering a NV4500/5600 transplant. The Jeep clutch master cylinder and NV4500/5600 slave cylinder work well together.

definitely sounds like a bad master cylinder!!!