I hope you have not added any fluid except DOT 3 or DOT 4 brake fluid to the brake master cylinder.
Brake master cylinders have what is called a "residual pressure check valve" in the outlet gallery of the cylinder.
The purpose of this valve is to permit all but about 4 to 6 PSI of brake brake fluid pressure be returned to the master cylinder when the foot pedal is released. The remaining (residual) pressure is trapped in the brake circuit to keep the wheel cylinder rubber cup lips "inflated" and thus pressed tightly against the cylinder walls to minimize occurrence of leaks there.
It may also be possible for trash and sludge in the master cylinder bore to to have migrated to the residual check valve and interfere with it letting ANY pressure to relieve back through it.
If ever any petroleum based oil, or silicone based (DOT 5) brake fluid was poured into the brake master cylinder reservoir, the rubber residual pressure check valve has probably been ruined.

How long have you owned this lift? Has there been any work done on the lift recently? Usually the master cylinder linkage gets adjusted & it's good & doesn't need further adjustment until a master cylinder change.

It's not difficult to adjust if it needs to be. There should be at least a 1\2" free play the the pedal pad which you should be able to feel easily if you apply the brakes by hand. If there's less than that, chances are this will happen again.

Yes, there is no free play in the pedal. I released pressure by opening the bleeder on the brake drum and the breaks released. Still not sure why it suddenly got so tight. The clevis adjustment is in the same spot as it has been while it was working fine. i will keep an eye on it and see if it starts tightening up again. Thanks to all for the info and insight.

bbforks is most likely correct in that.
I will however add that the adjustment to correct for this must be made on the actual master cylinder pushrod clevis, not on other pedal links or stops.
Aside from the pedal being super tight without any free play, the other indicator to this condition is that you might start out a tour of duty and the brakes only drag slightly, but as the drums and wheel cylinders heat up, the drag becomes more severe.

Brake pedal super tight? Do you mean that there is no free play in the application of the brakes- the pedal is hard to push immediately?

If so, the adjustment on the master cylinder application rod may need to be adjusted. If there's no free play, then the brakes can't "bleed" back to rest state & on each application of the brakes the system holds resisdual pressure which eventually hold the brakes on

Thanks for responding. Forward or reverse makes no difference..Actual break pedal is super tight....Parking break is disengaging. No loss of fluid in break cylinder. Thanks again

Are the brakes locked in forward & reverse, or do they release when you change direction?

Are you sure the parking brake is releasing?

Has the level of the brake fluid in the master cylinder gone down?

Ok so as I said before the inching pedal works great. It even helped the breaks work better as well...Unfortunately today when I pressed the breaks they locked up and now they won't come unstuck. Every time I drive I have to press the gas pedal hard and the truck lurches forward and does not drive smoothly. Any Ideas? Thanks

Yep you nailed it. I replaced it and it holds great. Thanks a lot!

Thanks a lot! I will try that.

The inching pedal dumps pressure in the transmission- effectively putting the trans in nuetral so that you can raise the engine speed to use the hydraulics without fighting the trans.

If you're losing brake fluid in the inching master cylinder with no visible leaks, the fluid is going into the trans through the actual inching spool itself. The brake line on the inching side should go from the master cylinder, to a cylinder with multiple brake lines going to it on the front of the differential behind the upright. One of those brake lines should go to the left side of the trans (as sitting on the machine) to a little cylinder looking thing with a bleeder on the top. This is the inching spool- remove the brake line, the spool should unthread from the trans- replace the spool itself- Clark #2798420. Don't worry about the brake fluid in the trans- it's a very small amount compared to the fluid volume of the trans

Ok, so now I have the breaks working. However, the Inching pedal keeps using up fluid and it is not draining out on the floor or anywhere in the machine I can see. It has to be going somewhere. Any thoughts? Thanks

Yes it is a C500/YS60. Bleeders are on the top of the wheel hubs. Parking break works fairly well. I have the breaks working slightly but not up to par.
I believe it is an automatic. It has a high and low setting and a forward and reverse. So I believe that means automatic.
Never heard of an inching pedal before. Now that you mentioned it I will research it in full. Just found a diagram on an inching pedal. That is exactly what it is! Thanks

Is the model a C500-YS60? Where are the brake bleeders exactly- on top of the wheel hubs or under the floorboard on top of either side of the transaxle? The parkiing brake is a seperate drum brake on the rear right side of the trans. Is the parking brake cable adjusted correctly? When energizing the parking brake the handle should feel a bit of increasing resistance as the handle is being pulled rearward.

As far as the clutch, is the unit a manual or automatic? Sometimes folks refer to the inching pedal as the clutch pedal. That could be a few things depending on your answer