For those looking to upgrade the MOSFET on the XP 3A, here are the location of the N-Fets and P-Fets.
You can replace the N-FET with the DMN2041. This takes the resistance of the original FETs from approximately 30 mOhms down to 26 mOhms or even 13 mOhm stacked as mentioned below.
The P-FET can be replaced with the DMP2035. The P-FETs original resistance is approximately 60 mOhm. Replaced with the better quality FETs, you take it down to ~30 mOhm or 15 mOhm stacked. Quite a difference. Less resistance means less heat and more power going to the motors.
As alluded to above, stacking two or three of them together effectively lowers the resistance and basically “upgrade” the ESC so it can handle more current through them. Here’s a great tutorial from AtomicMods that demonstrate how to stack FETs.
See this awesome thread and work by Steffen, author of BLHeli brushless ESC firmware code where I gleamed much of this information. Look for more post on the subject as I attempt to convert a mSR X and Xieda 9958 to utilize a brushless motor.