Gas millage affected by alltitude?

[BillH]

Question? I`ve had 3 olds Delta 88`s over the years, my latest is from Florida.
The other 2 got around 600klm per tank (ontario cars), this one gets 480 per tank. I was in florida last April with it and it got 650 per tank. I thought it was a computer thing, so I swaped in one from toronto but still get the same millage. Is there something else that could be causing this?

Bill.

2001 Tahoe LT

[TrailLeadr]

Are they all the same year? There are a lot of variables that could cause that.
Different tire size. Engine strength (weak/low compression on a couple cyls) just to name a couple different variables.

[BillH]

2 1987s and this ones a 1990. all 3.8l and the same tire size. I can have the comprestion checked