The day after the fall
Did another drain and fill like [MENTION=139000]phattyduck[/MENTION] recommended, drained out just over 2 quarts and added one quart back. Drove it around to heat it up and checked it again - low.
Long story short, it took another whole quart and 2/3rds more to reach the top hot mark when hot and I used Castrol Transmax Import per [MENTION=69868]LittleCaesar[/MENTION] that I bought at AutoZone - Walmart was out of it. Checked level again today, mid-day after driving in traffic for an hour, full. Overall, it was behaving well. The hard shifting was likely due to fluid level, but what was weird is the day before it was reading high, like over the full mark. I think the dipstick angle is shallow into the pan and leaving the stick in too long after wiping it gives a false-high reading - just wipe, stab, pull and read.
With the correct fluid level the clunking is greatly reduced, although still present at times (and interestingly at other times not) it's not as bad as it seemed. Just like hand sanitizer, paranoia was a big ingredient in my experience. Not sure if I should delete this thread or my entire account :wow:
[MENTION=134884]RonJR[/MENTION] was right on, part of the clunk is the cumulative lash in the drive traing being taken up by the rotation of the drive shaft when shifting into gear then finally meeting resistance of the locker. Hypoid gears in an open diff just spin and even though the same effect is present, there is no jarring clunk to communicate it back through the drive train to the driver.
The same clunk sensation can be felt while driving, to a lesser extent, when releasing the throttle and getting back on it, the drive train slack will wind till it stops and clunks albeit less noticeable than when in park. To really minimize it while in gear, a very light and slow approach on the pedal is required, stabbing the throttle is gonna make it clunk. This holds true both while rolling and while leaving a stop (truck in gear). Lightly approach the throttle and slowly increase - which coincidentally is also more fuel-efficient than a lead-footed launching stab at the pedal.
In summary, 2/3rds of this thread was self-induced paranoia fueled by something new and different. That does not mean my transmissions is A-OKAY, so I will probably continue with a drain and fill regimen until I experience actual ill effects beyond misreading the dipstick and underfilling the pan.
:ban:
Next on the agenda:
-flush the power steering system
-rear diff fluid to 85-140W