Steering switch not hitting?
When you say "steer left it locks up and becomes nearly impossible to turn" are you saying the truck will not swing left or are you saying it swings but then will not drive?
When you say "truck also gets very hot whilst trying to steer", are you saying the operator feels heat, or is it in the control panel or under the battery?
My "instant w.a.g.": you may have a bad motor, most likely a connection to the power cable, and will be pulling the battery out to look. it may even run when in the air, but under a load starts to have an open.