Neither was lockup. The 904 should free up some HP with the smaller internals. The lower first gear makes it get moving easier. Hard to speak to mileage since the truck was getting tuned up as it went. Comparing it to how it was running when I got it (cheap) because the 727 was fading isn't a fair comparison. Simply put, the 904 will soak up less power and last a good long time, but the 727 will last longer and tolerate heavier duty. It's all in how you wanna use it.
I agree with ya, i'm famalier those things, as i was a trans. mechanic the first 4 1/2 years of my 28 years as a mechanic, and i have a 904 lock up to build and a possible chance of getting a A500. I just don't know if there is any milage gain's. I feel like it should but i know how somtimes that thing's that should aren't just that, but thanks for your reply anyway.