I'm sure there will be instances of D1105's overheating in many applications as well as GM3500D's but your question is fairly academic.
Yes, flushing the cooling system may cure it - if the cooling system is blocked. Is your's showing signs of blockage?
Overheating can be caused by many factors including:
Leaky radiator.
Failed radiator cap.
Slipping fan belt.
Damaged/missing fan blades.
Broken water-pump impellor.
Blown head gasket.
Cracked cylinder head.
Low oil level.
Retarded engine timing.
Excessive load. etc. etc.
Blocked radiator...
Given that you're at a Golf Course my first question would be - Is your radiator core clear of grass debris?
Do you blow it out daily? I mean really blow it with compressed air to be immaculately clean?
Did you test the old thermostat? Did it fail the test? If it didn't fail testing it wasn't the cause of the overheating.
Have you "Searched" the forum for Overheating discussions? Many snippets of advice here already.
Diagnostics is a process of sequential logic.
Make sure you refill with 50% corrosion inhibitor when flushing the rad if you do. (Does the cooling system currently have nice clean anti-freeze or is the fluid all rusty-coloured?)