Welcome, I am Chris (aka-Moose)
A reading of 142 Hz is about 5700 above sea level
A reading of 146 Hz is about 4200 above sea level
I would not worry about those readings, there pretty darn close. Normally when this sensor fails its a huge difference from actual elevation. I also do not feel like this is causing the transmission issues.
Stalling when using manual 1st is caused by a pressure loss issue within the transmission valve body in this gear resulting in the converter starving and auto engaging the converter clutch. A harsh 2-3 shift can also be a valve body concern. You need to remove the valve and accumulator bodies and inspect the valves bores and springs for damage.
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