It's not the Gmail app itself, ROM or Store version. It's Play Services.
The Gmail fix is relatively simple and works every time (so far, I, and 6 of my friends, have used it):
Settings > App Manager > All > Google Play Services
Undo all updates. It will tell you it's installing the "factory" version of it. Hit OK.
Gmail (black Rom version) will [should] work.
Then, I went into Google Play Store settings and UNchecked all auto-updates so they can't slam me into non-working updates anymore.
When you run Maps and a few other Google apps, it'll put a little alert on your Noti Bar that the app NEEDS the newer version of Services...it doesn't...they all work perfectly so ignore the warning until a new Services gets released.