New model army and it's not even close. I'm so glad its not needed to complete the game, though it did stop me getting 100%. Some of the driving school missions are pretty diffcult to crack.
I reached a hard stop in IV with a nighttime motorcycle chase pretty late in the game. No idea what the mission was called, but nightime racing in IV was no fun at all (fudge you, Bruce!). TBOGT had a difficult combat mission where there's so many enemies its difficult to avoid getting killed, and it's a bit like the woodmill rescue mission in V. I don't recall anything else in V giving me much trouble. Does the hunting minigame count?
Vice city stories I tooled up with a minigun and killed the big bad in about 5 seconds

pretty sure that shouldn't be allowed