Before I start, yes, the 747 DOES WORK but the 777-300ER doesn't.

Basically, in the cockpit, there are no GPWS callouts (2500, 1000, 500 etc.) BUT, in the outside view it DOES work.

Mods I use are as follows: Salty Sims 747 Stable Version, CS 777 Improvement Mod, Salty compatibility mod, CS-777-300ER Flight Model Fix and FFS+ Sound mod

[b][i]PROOF: twitter.com/i/status/1470174943732240391 - OUTSIDE VIEW
twitter.com/i/status/1470173455026991110 - INSIDE/COCKPIT VIEW
The proof is on my Twitter account where I've posted a clip inside the cockpit and one outside the cockpit.