Disable AFM for $0: The M5 Method for 6-Speed Trucks

[BlueV8]

Disclosure: BlueV8 is a Supporting Vendor and sells plug-in AFM/DFM disablers.

 

Before you spend a dime with us — or with anyone — try the AFM disabler GM already built into your truck. It's the shifter, and it's free.

⏱ The 10-second version

Skip the M5 method if:

• Most of your miles are highway — M5 locks out 6th gear, so you cruise at higher RPM and burn more fuel
• You already know you'll forget — it only works if you do it every single drive
• Your lifters are already ticking — nothing that switches AFM off repairs existing damage
• You already run a tune or disabler — this would be doing the same job twice

Worth trying if:

• You want AFM off today, for exactly $0
• You want to test-drive V8-only life before buying anything
• Your driving is mostly town and short trips, where 6th gear barely matters
• Your truck is leased or under warranty and you won't touch the ECM — this is zero hardware, zero software

The whole trick, in one paragraph

Owners across GM forums keep reporting the same pattern: put the transmission in manual / range-select mode, pick M5 or lower, and AFM never activates — the truck stays in V8 the whole drive. Bump it up to M6 and V4 mode comes right back. Two of the cleaner threads on it are here and here.

GM has never documented this behavior, so file it under "strong owner consensus," not gospel. The good news: it takes exactly one drive to verify on your own truck. Steps below.

What "free" actually costs

Effort, every drive. It's a routine, not a setting. Shift to M, tap up to 5, every time you get in. There is no set-and-forget here.

6th gear. When GM shipped trucks with AFM/DFM switched off during the 2021 chip shortage, its own estimate of the penalty was about 1 MPG — and those trucks kept every gear. In M5 you're also giving up overdrive, so expect the highway hit to be bigger than that.

Patience. One Tahoe owner ran the L5 routine for two months, then got tired of it and bought a plug-in disabler — he had an extended warranty, so flashing a tune was off the table. That's not a knock on the method. That's just what month two feels like.

 

I put together the full instructions, limitations, and links to the original owner discussions here:

https://www.bluev8.com/blogs/news/how-to-disable-afm-for-free-the-m5-method

[Snowcamo]

Would be cool if someone made something most people would like.

 

Like a plug in tune that is to the end users desire minus messing with the throttle petal factory settings. Sport, economy and WFOT.