Just as a point of clarification, the strong nuclear force drops off dramatically once you go "outside" the nucleus. It's effectively zero long before you reach the Bohr radius. It basically holds the nucleus together (because positively charged protons wouldn't normally like being in close proximity due to repulsion of like charges). The weak force seems to govern radioactive decay, and is manifest in both photons and particles (which, I suppose, you could lump as "radiation" in common parlance).

I've been reading a few things that are asserting that there is no GUT because gravitation cannot be reconciled with QM. Here's a pretty tame article that doesn't get too far into the weeds:

space.com - Wavy space time theory quantum mechanics general relativity

Wouldn't be the first time we were pursuing something that wasn't soluble. Newton spent a large part of his life trying to explain the wave characteristics of light in terms of particles ("corpuscles"). We later discovered the dual nature of light. We also tried to find the medium in which light waves propagated, again to no avail (because it doesn't work like that for light...though this latter work led to the interferometer).

Maybe gravity is NOT united with the other three forces, and so we're chasing something that isn't so.