Chevy Silverado 1500 Overheating Issue

I have a 2006 Pickup, 5.3L with an overheating issue. Initially, the overheating was intermittent, so i figured it was a thermostat (sticking at times). I replaced the thermostat and the problem still persisted, and actually the engine seemed to be overheating more frequently. I then changed the water pump (the old pump was not leaking coolant) and the engine is still overheating. The engine overheats very quickly (within a few minutes) and the coolant boils in the over-flow reservior.
IMO is seems like the coolant isn't even circulating through the engine. I am at a loss as to what the problem could be? Any help would be greatly appreciated.
BTW, the coolant in the reservoir is very clean, so I assume the radiator is as well. This vehicle has never had any radiator damage or had the unit flushed.
Thanks
Comments
From your symptoms, I would have to strongly suspect a head gasket or cracked cylinder head issue, because of how quickly the engine overheats. This suggests to me that the coolant is being boiled by ADDED heat, not just normal engine operation.
You can test for a bad head gasket by using a coolant pressure pump. You pump it up to a few pounds more than your radiator cap pressure reading, and while holding pressure in the system, extract the spark plugs one by one and look for coolant on them.
You can also look for water/oil goop on the end of the oil dipstick, but that's often not an accurate test.
Another good test that requires some special equipment is a cylinder leakdown test, where air pressure is injected into the cylinder.
Overheating can sometimes be very tricky to diagnose. It's actually part of a rather complex system of interdependent parts, so it might take a while to narrow it down.
but you either have a bad head gasket or a massive blockage in the water galleys somewhere in there.
Ah, chat typos. We're all pretty fluent in those nowadays.
You do have 4 hours to edit your posts here.