At 190K, your clock is ticking. Keeping the system disengaged (lifters locked) certainly seems to be the second best option next to a mechanical deletion of the system. Have you owned your '08 for all 190K miles or at least know its maintenance and repair history? An '08 would have the oldest rendition of the AFM components unless it has been upgraded, which is usually done following a failure. Upgrades were made to the lifters and VLOM and a couple other parts were revised during this generation starting in 2010-2011. Regardless, the fuel savings will never outweigh the risk of keeping AFM active.
Instead of a plug-in device, I'd strongly recommend having AFM tuned out. You can have this done for as little as $50 plus cost of shipping your PCM (~$15?). You'll just have to remove you PCM and have your Tahoe out of commission for a few days. IMO, still a far better option than $200+ for a plug-in module that will still require tending to. For $65, you can "set it and forget it". And if you ever have a mechanical failure and need to do a delete, the PCM won't require any programming- swap the parts and get back on the road.
Go here:
https://lt1swap.com/afm_delete.htm
Also, do you monitor your oil level? AFM contributes to oil consumption but there's also an upgraded driver side valve cover that really helps, too. This is another item introduced around 2010 that yours should get if it hasn't gotten it already.
Speaking of oil levels, a huge killer of the AFM system is dirty oil due to improper maintenance. The system is sensitive to sludge. Yours lasting so long tells me you keep up clean oil in it or are just lucky. AFM disabled or not, stay on top of your oil changes.