The question is, for an automatic transmission, when parking on an incline, is it safe/proper/good to place the vehicle in Park before applying the parking brake?
I believe this is improper because the parking pawl is not meant to hold such weight, but others disagree with me.

I found this interesting in the H3 manual:
Park Brake and P (Park)
Mechanism Check
Park on a fairly steep hill, with the vehicle facing downhill. Keeping
your foot on the regular brake, set the parking brake.
.
To check the parking brake's holding ability: With the engine
running and the transmission in N (Neutral), slowly remove foot
pressure from the regular brake pedal. Do this until the vehicle is
held by the parking brake only.
.
To check the P (Park) mechanism's holding ability:
With the engine running, shift to P (Park). Then release the
parking brake followed by the regular brake.

 

Parking on my driveway incline, the 4l60E holds the 3 secured tight without e-brake! If you park on a "steep" incline get a set of

Heavy Duty Wheel Chocks

Heavy Duty Wheel Chocks

, parking brake not required.

 

A 4L60 has a a very strong parking pawl that engages directly into the splined ring gear which is directly connected to the transmissions output shaft. When you put the shifter in park the pawl locks into a slot in the ring gear.

This connection is so strong you can literally drag a hummer on all 4 wheels (flat bed tow truck drivers have done this after a bad wreck). If you are on a severe incline it helps to step on the main brake and set the parking brake then place the vehicle in park.

This will make it easier to take the vehicle out of park as it removes the pressure from the pawl and prevents a lock condition. Here's a picture to give you a visual:

 

@hummerz Is the gearshift hard to move when the H3 is pointed uphill or downhill? Of course, I don't know how steep your incline is ...

@H2-SUT Thanks for the info - I didn't realize they were that sturdy on the 4L60. I wonder how the pawl and gear wear when under load.

 

No problem moving the shifter on my driveway @ 10% slope/grade. If you have a hard time moving the shifter, inspect/lubricate the shifter/cable/linkage.

 

As others have noted, automatic transmission parking paws are quite robust, but it makes sense to protect them whenever possible. On steep inclines, I'd follow @H2-SUT advice - apply the parking brake first to take pressure off the pawl before shifting to Park. That gentle approach seems like a good balance of function and longevity for the vehicle.