Well you have been grinding a lot and the game isn't made for that because there's no need for it. Personally I thought I was grinding because I spent many hours not really achieving much beyond extracting a few high level soldiers, but you've taken it to a whole other level! I mean, I'm at 94 hours played and something like 64% complete, you must still be in the 20% range with 300+ hours by now?
Not that there's anything wrong with that if you're still enjoying it, but the game is set up to give you a drip feed of new gear as you encounter new situations, the blueprints and specialists are just a more rigid way of enforcing the feed, otherwise you're encouraged to just keep playing to accumulate GMP and soldiers with better skills to improve your team levels which are a softer limit to your progress (because you can grind around it until every member of each team is the highest possible rank available to you). You can grind if you want but it just means that drip feed becomes a stone wall where you get nothing new for hours, you can't spend GMP even though you actually want to (p.s. have you tried deploying with the most expensive possible loadout? How much does it cost?) and, well, you end up in this situation.
I'm sure the various caps exist for a reason, I mean there has to be a limit somewhere and most people would only actually hit said limit after buying everything, at which point the limit won't matter. I somehow doubt you'll run out of GMP anyway, though, with over 100 tanks that sell for 100,000 each...
When I finish this playthrough - I haven't been in the same county as my PC for a couple of weeks - I want to start the absolute opposite playthrough to yours. I want to only return to Mother Base when the game makes me, deploy only with the cheapest possible loadout, develop nothing, use no buddies except D-Horse, Fulton no one (except for those I have to Fulton) and generally see if it's possible to beat the game that way. It might be fun, it might also be awful, who knows. I'll record the whole thing if I can. And if it's interesting.
I've always HATED not getting the "fun" weapons in games until the end, when the game is over. So, I grind when I can to develop money or whatever to buy and upgrade what I need for the fun weapons. I have them now, so time and effort very well spent.
There are some weapons I still want, but have to wait. So, I get a little of part a and a little of part b. I have pretty much a version of every weapon in the game and I want to try them all. That takes money. In this case GMP. I still get the fun of waiting to build and have something, while playing with weapons that are fun.
So, Africa is pretty awesome. I like it better than Afghanistan. How about you?
I finally got the D-Walker and I'm not to crazy for it. The F-Ballista thing is fun, but just 8 shots? I think I'll stick to Cloppity and DD. Made all the upgrades I could and still have plenty of GMP left. What's the most fun thing to do with D-Walker, next to F-B soldiers from far away?
Finally got the Legendary Gunsmith. Still have yet to see the different types of scopes in action, but 2x8 Range Finding scope is pretty awesome. Now, I just wish I knew the bullet/tranq ballistics to apply it to the distance, and I'd be totally in love with this game. Can't wait to develop the sleep gas grenade launcher that fits under the rifle. A non-lethal attachment to a lethal rifle sounds fantastic. And I LOVE having a medium suppressor for a change! To have a rifle/pistol that runs out of ammo before your suppressor conks out is just great!
Pitch Dark was a total pain in the ass. DD kept dying on me! I have no idea why. He'd just go run off on his own and drown, I guess. He never got shot, or anything. Just ran off, and died several times. I guess I relied on his marked enemies too much, for when DD is gone, so are his marked enemies. Lessoned learned. Never did find the blue print, but I ran out of there before I could check all the doors.
I haven't gone for the translator (Episode 14: Lingua Franca), yet. I wanted to explore a bit. But, I'm not going to do what I did in Afghanistan. Like taking out objectives before the episode/mission even starts. Want to avoid another C2W.
So, any fun or interesting things to do or look out for in Africa? Things I should do first?
), I still don't have an S rank for that episode. Oh, I've received the S rank, a bunch of times, but it only show a stupid - as my rating. 
the Extreme
