Metal Gear Solid V: The Phantom Pain Message Board  

The reason that your GMP is maxed out at 5 million is because you are running it in offline mode. When you are in online mode it sends your extra GMP to your FOB's. At least that is what it does with mine.

Exactly, but I could push it above 5mil, however I'm no longer able to do this. I guess, they "fixed" something in the game, and as I said in my OP, it's not an issue, just really wanted to clear up that it wasn't a problem with the trainer, not that I expected it to be, but I HAD to ask.

Hmm, for me the problem is if I am in online mode, I can adjust as much GMP as I want but When I start a mission or change a scene, my GMP drops back to negative(which I guess would be my original GMP value). It seems the server holds my actual funds and I can not change it. If I am in offline mode, I can not change my GMP at all.

Sounds like they are cracking down then. I stopped playing the game because it not finished and never will be.

If the GMP option is not working for you, you can try using the Massive Materials and then sell to the max GMP. I tried it and it works. cheers!