AFR gauge with o2 sensor worth it or not?
It's a great tool and worth the money if you take the time to tune. A 2500 ft change in altitude is going to have you running in circles. A holley type carb will require around a 2 jet size change to keep the AFR ideal. You might want to go FITech if you drive a lot with those kind of altitude changes.
Uh, if he drops from 7,000 feet to 5,500 feet that's only a 1,500 foot drop, not a 2,500 foot drop. The change in AFR isn't that bad even for a 2,500 foot change, it will be barely noticeable for a 1,500 ft change.
I drive my Duster through a 3,500 ft elevation change pretty regularly, at least once a month or so. Yes, you do notice a change in the AFR, but really it's not that bad. I was surprised it didn't change more. I've driven my car up to Lake Tahoe a few times, from where I start in Sacramento that's over 7,000 ft of elevation change over the pass. Again, sure, the car runs a bit rich of there, but it still runs ok. Going down in elevation is a little more troublesome because you'll run leaner. With a mild engine it probably isn't a big deal, I know I would have to richen my carb up if I was going down in elevation as much as I go up in elevation, but my engine is pushing the limits of pump fuel a bit so lean isn't a good thing.