2009 Cobalt SS running at 183-190 Fahrenheit

So my 2009 Cobalt doesn't seem to be moving coolant like
it should.   The return line to the overflow is getting supper
hot, but the top radiator hose gets warm.   The bottom hose
from the radiators to the engine is cold.    I've  check to see
if the radiator is clogged I even purge the system three
times to see if I had some trapped air. I have a brand new
LDK crate engine from zzperformance which has a brand
new thermostat and pump.    My  car typically runs at 183
to 190 fahrenheit.  I've been reading and people say that's
to low, and the thermostat won't open. I'm just puzzled why
the return to the overflow is so hot and the lines to and
from the radiator are not as hot/cold.   Any hints?