You didn't say if all 3 overheat or is it just 1 of them.
Flashlight shining through the radiator from one side and someone looking on the other, check the whole radiator for dirt this way. Light should shine through or be blocked showing you where to clean. Be careful as radiators are easily damaged.
Low fluid levels, when machine is cold in the morning the rad cap can be removed and it should be full as well as some fluid in the catch tank. If you've been using water to top them up, this is not as good as anti-freeze. Drain system and replace with 50/50 mix of water and anti-freeze.
I would re-torque the head bolts just to see if it helps. Can't hurt.
But most likely suspect could be thermostats. Try to find ones that are a lower temperature setting or at least replace with new ones.
Last thought, jack machine up and make sure the brakes are not dragging or stuck on. Wheels should turn freely with a little effort but not much effort.
Good luck.
Let us know what you find.
Unless the weather is extremely hot they should be able to handle this type of work.