Why did Tesla Model 3 fuel economy dropped from 142 mpge to 132 mpge?

Different batteries, different chemistry...
Iirc, Tesla also switched to a bigger cell, to increase density.

From:
Here Are The 2022 Tesla Model 3 EPA Range And Efficiency Ratings
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Here Are The 2022 Tesla Model 3 EPA Range And Efficiency Ratings
The entry-level version now has more range than ever, but the efficiency is lower.
Dec 22, 2021 at 9:24am ET

The U.S. Environmental Protection Agency (EPA) has listed the new range and efficiency ratings for the 2022 model year Tesla Model 3, which is available in three versions: RWD (the new Standard Range Plus equivalent), Long Range (AWD) and Performance (LR AWD).

2022 Tesla Model 3 RWD 18"
The entry-level Tesla Model 3 RWD is equipped with the Lithium Iron Phosphate (LFP) battery chemistry, as the manufacturer is in a process of a global switch to LFP in all base versions of Model 3/Model Y.
This battery pack has probably a slightly higher capacity, but because of lower energy density, it's also heavier, which affects efficiency (it's lower now).

From the consumer perspective, it might be a good change, because the range is slightly higher, and the LFP battery chemistry is much more tolerant to a high state of charge.

As far as we know, users can charge the LFP battery version to 100% State of Charge (SOC) within the available SOC window, without much worry about its longevity. In the case of NCA (a higher voltage chemistry), the default recommended daily charging level is close to 90%.

The 2022 Tesla Model 3 RWD with standard 18" wheels has an EPA Combined range of 272 miles (438 km), but it's over 260 miles (419 km) in the EPA Highway test.

According to Tesla, the switch to 19" wheels will lower the EPA Combined range to 267 miles (430 km) - by 6 miles or 2.2%.


Now, let's take a look at the comparison of the new LFP and outgoing NCA battery versions.
The battery capacity is unknown (but a level of 60 kWh, ± a few kWh). What we can see is a few percent increase in range, but interestingly - the EPA Highway range is 11% higher. That's something that we would like to check in the InsideEVs' 70 mph range test.
While the top speed is the same, the acceleration of the new Model 3 RWD is slower.

As we hinted at previously, the efficiency (including charging losses) of the Model 3 RWD with a heavier battery is lower by up to 7-8%:
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