Usually, the R&P will have the numbers on the ring gear. Like this... 14:43 or a 3.08 gear ratio. Yours could be 10:41 for 4.10 ratio or 11:41 for a 3.73 ratio.
Yep, aftermarket AC. Factory AC with have the unit that looks like this in the engine compartment. The factory HVAC selector will also have settings for MAX, Bi-Level, and vent.
How much gas did you have in the tank? The level of fuel effects how hot the FP gets. Being in the desert, summertime temps were a good culprit to killing the FP on a low tank of gas.
So, do me a favor since you have a lathe. Attach one side of the axle to the lathe and leave the other unattached. See how much runout there is.
I understand both sides are supported, one by the carrier and the other by the axle bearing. But a bent axle will eventually start wearing parts...
Think about this...
the length of 30", with a tiny bend in the middle, as it spins the bend will want to force itself outward creating a vibration.
A driveline is balanced just like a tire is balanced to 0 so there is not vibration. Same goes for axle shafts.