My SR5 has 110k on my T4R at the time of install. Other than a shift kit I have no other mods to the drivetrain.
First of all let me say the kit was very well put together with quality parts. There was no need to go to the parts house for anything during the install. The entire process took me 24hrs total across three different days. I could have probably shaved 6hrs or so off of that but I was enjoying myself and didn't get in a rush.
As for performance, it has exceeded my expectations. I am running Wildpeak 285/75 E rated tires on Trail wheels. I was around 16mpg no matter hwy or city before install. I now get around 15 in the city and almost 19 on the highway at 75. Push it to 80mph and I'll get 17ish.
Plenty of usable power across all gears. It didn't drastically improve take off but there is a noticeable difference. It will basically drive like a stock truck if you want until you get in the throttle. It's not "touchy" or "jumpy". Just nice and smooth. In short it has the power it should have come with from the factory. I've put about 2k miles on it with no complaints.