AFM has nothing to do with tranny. As for tuner, get a used diablosport off ebay.
I picked up one a few years ago for $250 or so, and I have used it on my last 2 rigs.
You can tune, change tire size & pedal sensitivity, and turn off AFM or speed limiter plus custom tunes. Best bang for buck ...
Engine Half@$$ does have something to do with the transmission ... tuning.
Torque converter clutch slip in cars with Engine Half@$$ is higher than in 2500-&-up trucks
that lack Engine Half@$$.
So when your diablosport disables Engine Half@$$, it may not reduce the TCC slip.
So even if your engine is always a V8, the TCC will still slip and wear out eventually,
which will eventually take out the 6L80.
A full tune from a reputable human being will permanently disable Engine Half@$$,
AND also retune the 6L80 to correct the TCC slip, among many other things that can be
custom suited to your tastes, including tire size & pedal sensitivity.