No clue what's wrong with my 2013 G37
 

So while driving, mainly in DS or manual mode (G37 sedan/automatic), but it has started losing the power while driving in just normal drive mode now. In DS or manual mode, my car will clunk and just completely power off and turn back on. It's never for a long amount of time, usually about a second or so and there's not always a clunk which makes me think it's not the tranny (god i hope it's not the ****in' tranny again). I got my alternator and battery replaced recently and months prior to THAT replacement, I got an expensive new tranny. There's no knocking, no noises, idles perfectly fine when stopped, turns on and off perfectly fine, but occasionally I'll shut the car off and every single electronic in it will stop. So for example, I'll shut the car off to get out and the car will lock me inside it and I have to manually open the lock. The lock buttons inside the car stop working, I can't turn it back on, the key fob won't work even when I put the fob into the little key slot, and I have to get it jumped. 5-10 seconds on jumpers and it turns on like nothing was wrong with it immediately and again, still no sounds, even when the hood is up. No corrosion on the battery either. Is it the ECU? Battery defect maybe? If I try to manually shift it, I notice the clunk anywhere around 2nd-4th gear including on downshifts and in DS mode, it's kinda hard to tell what gear it's in, but I'm assuming it's around that same shift range. It still accelerates fine and everything. It has been doing this for about a month now. I do also have a radar detector in my car plugged into the car outlet up front next to what I use as a coin area and that will sometimes just reset randomly.

I would hardly call them mods, but I have K&N filters and Kinetic HFCs because OEM cats are expensive.

Have you checked the ground connections from the battery? If the terminals haven't been cleaned or replaced, there's a chance they are a weak link in the overall power grid. It sounds like something is disrupting the power supply while the car is in motion, so start with the simple items and work your way up from there.

What's the order in which I should be checking the issues? So, starting with the ground connection, if that isn't it, what's the next few things to check? Also, what does checking the ground cables entail? Do I just remove the battery and they're visible, or is there more to remove prior?