These are a decent servo that work well on 6V:
https://www.amazon.com/dp/B079HZL171/
300oz/in @6V and waterproof.
I ran a single one in my brushless revo for quite a while with 3.8" trenchers on it. It had plenty of power. I run one now on my stampede 4x4 with 3.8" LP MT tires on it and it...