The thing the trans guys don't get is that we only run overdrive for a few seconds, we're not pulling a house up the side of a mountain.
With your engine at 7k the Gear Vendor output would be 8540 RPM & was working ok Right? That's a planetary just like the 4L80! If ya can't stand to own a 4L80 then park the Gear Vendor on the back of a 400.
With a 4L80 you can run a converter & a lockup switch & you don't need an ECU, with a 400 you either run a converter or a direct drive, you can't have both.
Don't over think it Mate!
Sid.