It's a 94 K1500 with Auto transmission silverado with 202000 miles on it. The truck is running temps around 150 to 185 when going down the highway or in light traffic. However when it's 5:00p & I'm sitting idle in traffic it gets up around 220 degrees.

I flushed the radiator last night -- entire system flush & refilled. My fan clutch is operating correctly (moving in & out,,,increasing when rpms increase.
Not sure if it could be a stuck thermostat or bad water pump.

When I did the flush last night I noticed that the water wasn't "swirling", but more or less bubbling up and then back down.

Is this a clogged radiator or bad water pump.....or stuck thermostat?

 

sounds more to me like a thremostat, since my 87 did the exact same thing, and it was the thermostat sure enough.