Also check your ing timing, the Cat 1404 eng is the same, have seen the same conditions with retarded timing...

low power?
might want to check valve clearances too
Exhaust:.025in (0.64mm)
Intake:.015in (0.38mm)

i could not find a cylinder compression figure
the book just has a cylinder leak test and says that all compression between cylinders should not vary more than 20%. I'm sure its in some obscure corner of a section in there...i just didn't see it.

There also was a large section on how to adjust the fuel system which could also cause low power situations.

a 'larger-ish' vac. line from the valve cover to the intake.

haven't checked the pcv valve yet. where is it located?

replaced the PCV valve yet? if you have so much blow-by that the oil fill cap has blown off, you are without a doubt also forcing oil out the seals including the front and rear main seals. either your piston rings are so worn out that you are scaring the cylinder walls, or your not recirculating the air that is in the crankcase. while the 1 cylinder is a lot lower than the other 3, I would not really expect that to be where your lack of power problem is, more likely the lack of vacuum through the PCV valve circuit, and the leak of vac through the air intake where the pcv should be hooked up.
when you say "the governor is working", can you describe a little more how you know it is working correctly?

The governor is working. There is a lot of blowby. even blew off the oil filler cap today.

It is a Hercules.

If the governor is broken, then even if the carb's throttle plate is open the governor's my not be causing low power.

are you sure it's a CAT engine!don't recall running into any DAEWOO trucks with CAT engines in them???
Possibly a Hercules engine or a Mitsubishi ???

I will have to get the serial #. It is a G25s. Hours? good question, meter broke years ago. It is the original engine in a 20 year old machine.

What's the full model and serial number of the truck? How many hours are on it?

compression?