they had different gear ratios in cavaliers and malibus definitely wasn't a towing factor there. wasn't specific to trims either as you could find different ratios throughout. gm doesn't even like to market thier own performance options let alone allowing dealerships to market expensive indepth option changes. hell sometimes dealerships wont even remove options you dont want. if they allowed dealerships the ability to swap tunes so readily to a more performance related tune they would just look like idiots. all the time they have invested trying to squash anything relating to modifying thier vehicles outside of what they already offer. now granted finding a direct statement from gm suggesting they distribute cars to fit an area isn't going to happen. surf enough gm forums you might notice a trend where people in certain areas who want #.## gear ratio setup can't seem to find it. yet people in a different area have that version in spades. bit of a conspiracy theory i geuss but it was also odd an individual couldn't buy said part themselves and have the swap done on thier dime. gm does too much wierd stuff sometimes and it's actually something that makes sense in a marketing point. build a vehicle and tweek it slightly so it fits the area its sold in better.
cavaliers and the sunfire where twins, they had 3 trim levels including the Z24 (I had a cavalier), they also had different engine's or generations of engines and a 3 speed, 4 speed and 5 speed transmissions, a 2 door, 3 door (hatchback) and a 4 door wagon, I thought we were talking about the SUV's but there are any number of reason's why gm may give a different gear ratio anywhere from weight, size, transmission type and/or wheel diameter and/or intended use.
the computers in these things adapt for all types of environment including barometric pressure and generally those that live in at higher elevations get better performance and better mileage because the engine/pumps, etc do not have to work as hard which explains many reported differences
