I posted this in "Transmission" and only got one response.I was recently told that you could put the low gears from a 4L80E directly into a TH400 and achieve a lower 1st gear (higher #) to aid your 60 foot times. Has anyone heard of or done this mod?

Haven't heard of that,
a 4L80 has the same 1,2, and 3rd gear ratio as a 400 so I doubt it's true, and if it was as much as I mess with them probabaly would have heard of it by now.