StrokeOutboard has decided to overheat whenever the
RPMS are around 1200-2000. Either side it cools off but in this range it
warms up fast. The water pump is working because it streams water ok.
Nothing seems to be bloking the intake.

When you say overheating, do you mean the audible alarm comes on? Do you have a
guage that reads hot?
Does it have a water pressure guage? if so what is the pressure at this rpm?
The impellor should be changed yearly, so that a logical place to start.

More questions. What hull is the motor on?
I assume your hull is "mushing' at that speed. Not on plane, just moving a lot
of water.
Some boats were known to get hot running at those rpm's. The hull diverts the
water creating an air pocket allowing temps to rise.
You might try changing the trim angle and see what happens.

BR