Just use a fan. There is no reason you should change to a lower kv motor when the esc can handle much higher kv motors. It's gonna get hot, there's probably little to no airflow getting to your esc. If putting a fan on it is a bandaid fix, then they shouldn't be coupling 5700 motors with the esc and selling them to the offroad guys. I'd personally disable your punch control, set your motor timing to the lowest, and set your start power to high if you can use throttle control to overcome all this. And I'd use a fan. Or, you could throw away a perfectly good motor and spend more money on a slower motor like everyone else suggests.

I just don't see why everyone's so quick to have someone else change major pieces of hardware and not let them run what they want. A $5 fan will do wonders on a mamba esc. It did with mine, although I've never had the luxury of experiencing a thermal shutdown, it kept runnin deep into the 200s. And how is providing extra cooling/airflow a bandaid fix? Should I use less fans in my computer because maybe running 3ghz is the underlying cause of all this heat and I should toss that and get a pentium 2 with mmx? That'll run cooler and not require so much cooling.

Not trying to sound like an A$$ or anything, and I really know far less about r/c stuff than the vast majority, but my point is, if you go out and buy a 5700, which btw is probably the highest recommended offroad 10th scale motor I've seen, and you want to run it in your slash, the esc gets too hot and cuts out, don't you think maybe it just needs a little more air and since you say runing partial throttle is causing the heat and he doesn't have a chance to open her up. Then a fan would probably be ideal, because he already owns a 5700 (and yes in this partiuclar case a velineon, which is besides the point), can't open it up enough to keep it cool, a fan seems like a cheap fix that will protect your electronics from overheating, the esc can take the abuse! Just my $1.05