hypothetical liquid cooling system

[othello]

+1 to what Suicideneil suggested

The nitro motor you replaced in your lst2 was revving between 30000-35000rpm at max under load. This is also the ideal rpm range for a BL motor and will give you plenty of gearing options to adapt your motor to different driving conditions. Crazy fast with bigger pinions and better controlable + more likely to behave like a nitro motor with smaller pinions. With no need to use those ultra small pinions below 12t.

A 1521/1Y (1577kv) @ 22,2V (6s) would rev at 35000rpm and is a perfect fit. Your 1527/1D (2300kv) @ 22.2V might have hit 51000rpm. Your 9t pinion indicates that it was impossible to gear it apropriatly. Even with 5s it will rev @ 42500rpm. Still not easy to gear as it will require very small pinions and a powerfull ESC. At 2300kv it would be a better fit with 4s lipo, but this would demand very high Amps to get some decent power for your heavy truck: 2000-2500 Watt -> 150-200A @ 4s. I guess the MGM 224 is your best bet or maybe the MMM if it really can provide a 200A surge current.