Run MGSFIX to temporarily downgrade to D2 first on your PSP, complete the first mission on Peace Walker (Not the tutorial, the first proper mission) then your safe to run MGSNEVER and go back to D3 and continue playing. Enjoy!
I may try the new ram site, and download more RAM to my Switch. Not sure if ddr3 is the right ram
for it tho. Edit- no it uses floppy Ram, just like @AncientBoi