Throwing in my 2 cents. I've only got 30,000 miles. I am running a stage 2 but wasn't looking for full blown power and I've only got about 3500-4000 miles on this stage. Due to some fine tuning issues with my ProTune I decided to do the TGV delete. (My tuner and I saw some strange goings on regarding the TGV's) Since I didn't want to be throwing codes between installing the deletes and seeing my tuner I zip tied them in safe places and left them plugged in. The number one thing I noticed was the carbon build up on the valve flaps of the TGV's. After working on the tune for a while and doing a test drive, with what hopefully is the final tune for a while, I showed my tuner the gunk on the valves and he was really surprised considering my mileage. I also promptly ordered an AOS. I know there's varying opinions on AOS vs. dual catch cans etc. That's for another discussion. It is the route I chose to go for my own reasons.
I would highly suggest at minimum pulling the intake manifold and taking a look at the TGV's and, if they look gunked up, looking at your intake valves every 25-30,000 miles. This is the own of the downfalls of the DIT design combined with the stock oil recovery system. In my case a combination of carbon/oil build up, and probably a bad tank of gas from my regular Shell Station, was leading to top end knock when running my turbo at the same boost settings it was already at before the deletes. In short it is killing my octane retention. I will be doing the top end clean today! I'm literally out the door to pickup the kit after this post.:wink2:
I would definitely recommend doing the top end clean on the FA20DIT motors. If you are a hard runner or or tuning your car you probably want to look at adding an AOS or dual catch can setup.
If you are just a daily driver, make lots of short trips, or don't put very many miles on your car per year I would recommend doing it every 25-45k miles. Or at least once a year. You know what they say about an ounce of prevention...
If you live in a state like mine (CA) where we are stuck with E10 91 octane. I also suggest using a quality fuel system treatment/stabilizer/octane booster. By quality I mean a 100% petroleum product. Lucas has an octane booster and separately a ethanol stabilizer both of which are 100% petroleum products. Klotz makes great products and their octane booster is a pure petroleum and also helps to remove water from your fuel system. I was a long time Seafoam user but after having a weird experience in one of my cars I started doing more research on additives. They say their product is 100% petroleum but it isn't. If you read their MSDS it states it's up to 25% isopropyl alcohol. The whole point of using an additive is negate the problems the Ethanol is causing as far as water retention and gumming up the works.
Good information on some of the additives can be found here:
Is your gas additive safe with E10 fuel?
To sum up if your dealer doesn't offer it and you own a 2014+ XT I recommend you buy the kit online and use it preventatively. There is a lot of consistent information on the interwebs on why DI, especially turbocharged ones should do this preventively. One look at the back sides of the intake valve pictures will blow your mind!
If you have the 2.5 motor, even with the PZEV, 45-60k miles is probably a good call for the cleaning kit. Once again, just like "regular" oil maintenance, how you drive, where you drive and the fuel you use are all factors to take into consideration.
I prefer to error on the side of caution like changing my oil filters 1/2 between every oil change and even though I use high quality oil changing it 1000-1500 miles earlier than factory recommended.