RetCPO

If it ain't broke I'm not gonna fix it.

Shift to L and then toggle the + button on the gear shift, it will display L2 , L3 and so on. Stop when L9 is displayed on the dash. Transmission will then shift normally up to 9th gear. dfm will not activate.

2020 AT4 5.3 I run in L9, dfm won't kick in. Lose 10th gear but I'm not worried about mpg difference.

2020 AT4 5.3 w/dfm. I always drive in L9 dfm won't engage, but I do lose 10th gear. I'd rather have 8cyl all the time. Not sure what the mpg loss is on the highway but I'm not worried about it.

I just got back last Fri towed 1800 mi round trip in my 5.3 2020 AT4 towed 3500 lb trailer down 900 mi. empty and loaded up a 3700 lb. mustang and towed back. I'm guessing you have a tow package on your truck, when you twist the dial to the trailer icon on your dash a transmission temp gauge will pop up on your gauge display. I had no issues with engine temp or trans temp, engine temp stayed right in the middle and trans never went above 185 degrees and it was 85-95 degrees outside for a good portion of the trip. Your not going to have any problem towing 5000 lbs. Have a safe trip.

On the DFM website it states not compatible with 2019+ 6.2 with 10 Spd. I own 2020 AT4 with 5.3 10spd, and was interested in this disabler a few months ago, I went to the website and tried the "will this fit your vehicle" and when I put vehicle info in and got to the transmission selection there was no 10 Spd listed as an option to enter. I just went back to site today and 5.3 10spd is now listed as a fit. So it appears the problem regarding fitment is the 6.2 and not the 10spd. I would have thought the 10spd would have been the fitment issue not the engine size. Any 5.3 10spd guys out there running this disabler without any issues ?