best overhaul mods to make gta 5 story mode fun again?

Depends what got boring. For me it was the map feeling empty once the story was done, so this is roughly what I ended up running: LSPDFR if you want a completely different game - playing as a cop is basically its own campaign. A trainer (Menyoo or Simple Trainer) for spawning, weather, time of day and all that. NaturalVision Evolved or QuantV if your GPU can take it, the city looks like a different place. And a realistic handling mod, it changes the feel of every single chase. Most of these need Script Hook V, plus OpenIV for the ones that replace files. Two things that catch people out: keep a clean copy of the game folder before you start, and check every mod says it supports your version - legacy and enhanced aren't interchangeable, and Script Hook breaks after every Rockstar patch. Also keep it all well away from Online.