Now, granted, i have the diesel, but I thought my experience may have relevance.
I had to replaced my tranny not long after I did a bunch of simple power mods.... The original tranny was known to be the achille's heal of the 7.3's. I replaced it with what was at the time, one of the best reviewed trannies I could get, a Jasper Transmission Monsterbox.
First thing I noticed was firmer, harder shifts. I called Jasper, and they said this was intentional due to a firmer shift kit.
This was 11-ish years ago, never have had a single problem with it since, and I've always hauled heavy.