Should we be using the 2008 mortality tables being used for DB plans for cross-tested DC plans as well, rather than the 1983 GAM? If so, please be specific as to which ones. Thanks as always to anyone who can help.

the permissible mortality tables are listed in 1.401(a)(4)-12 Standard Mortality Tables
the last sentence says "applicable mortality tables under 417(e)(3)(A)(ii)(I) are also considered to be standard.

if you are not imputing disparity and everyone has the same ret age then it is a moot point because the APR becomes a constant.
use whatever permissible table helps you the best