Well, funny you mention the motor never heats up, this guy's motor never did either. Just the wires.
Perhaps you have a mate that could let you try one of his motors?
If you use it & the wires don't heat up, you know where the problem lies.
Good luck with it.
Losi SCTE SC4 Pro 4000kv, Tekin RX8, 2S
MP7.5 Kanai III Tekno Neu 1515/2.5D 1700kv MM 4S
LST 2 Carbon CC 1717 1Y 1580kv MM 6S
Futaba 3PKS Spektrum Pro