Overconditioned hair will generally be very soft but lifeless and limp. Curls will be waves, waves will be almost straight.

I fix overconditioned hair with a protein treatment (I use aloe, it's the only thing my hair tolerates).

Buildup is often described as feeling dirty, greasy, waxy, flaky, stiff.
remember, with all advice or suggestions for your hair, YMMV!!
My hair:
2b wavy, medium texture, low porosity, med-high density. Protein finicky.
My routine:
Cleansing: DCNP, every 4-5 days (occasionally use CJ cleansers).
RO: CJSC, occasionally use JCDC
Gel: KCCC, CJCIAB for 2nd day hair (sometimes third)

Heat is my friend: warm water rinses, steam caps, and diffuse dry. I love CLU cloths and my Denman.