What are the gap functions in the $AC$ hierarchy?
Razborov-Smolensky prove that the classes $\mathrm{AC}^0[p]$ and $\mathrm{AC}^0[q]$ are incomparable when $p$ and $q$ are distinct primes, which also implies
$$\mathrm{AC}^0\subsetneq\mathrm{AC}^0[p]\subsetneq\mathrm{ACC}$$
for prime $p$. That's about it: it is consistent with the present knowledge that uniform $\mathrm{AC}^0[6]$ coincides with all of the polynomial hierarchy PH, so no classes in between have been unconditionally separated (uniformly or nonuniformly).