Optimization vs modification... Let's discuss

Quick question before I begin:
Is the 4WD transfer case on our generation part-time or full-time? What I mean by this is: Is the front driveshaft only under power while the selector switch in is 4-hi/lo? Or does the selector switch only actuate a collar or slipper clutch at the differential, and the transfer case is sending power to both driveshafts 100% of the time. I ask because my last 4x4 was a 1995 Explorer XLT, and that had a 4WD system that used something along the lines of a vacuum-actuated slip-collar to lock the front driveshaft and front differential when demanded to do so; meaning that the transfer case itself was always in 4WD and both shafts were always spinning. I'd greatly appreciate any input on this.

So I'm currently working on optimizing my 2007 Tacoma TRD Pro (Speedway Blue, crew cab, long box) in the long run. Looking to start a discussion on optimizing a vehicle vs a more traditional modifying of a vehicle.

Firstly, what's your approach towards making changes to your vehicle? Are they more aesthetic-based, maximizing off-road capability, making the all-in-one apocalypse bugout vehicle, or something else? Why do you do it?

Secondly, how many of us genuinely care about maximizing fuel mileage at all costs, or is it something that doesn't really ever become a conscious thought? Am I strange for wanting to go that route?

I'm genuinely curious what people's opinions are, and what answers y'all come up with. In the meantime, allow me to explain my 3 pillars of thought process on the changes I'm making to my Tacoma.

1) Safety
2) Reliability/Ease of Maintenance
3) Efficiency of Motion

Any changes I make must meet at least one of these 3 requirements in order for me to consider it (I'm considering getting a bull bar for the front end during the spring/fall seasons primarily to deal with the uncertainty that is the rut). Now, most of the changes I'm making in the near future will primarily be fulfilling pillar #3, and that's where my quest starts to get interesting.

For example:
while there is no universal thumbrule ratio (that I can find)for rotational mass vs sprung mass, there is always a noticeable difference in feeling and responsiveness even when driving under normal conditions. And since rotational mass is a direct parasitic loss, reducing rotational mass at any point will ultimately mean that more of the engine's power is reaching the road per unit mass moved.
The stock 2007 4WD TRD Pro aluminum rims weigh 29 lbs each. The Michelin Defender LTX M/S tires currently on those rims (265/65R17) weigh 38 lbs each, combining for a total wheel weight of 67 lbs/wheel. The wheel package I'm replacing them with is a set of 17x8 Enkei Cyclone's weighing in at 26 lbs/rim (technically 25.9 lbs), wrapped in Michelin Primacy LTX (265/65R17) tires, weighing in at 31 lbs/tire. This nets a total wheel weight of 57 lbs, and a net weight loss of 10 lbs per wheel at each corner of the vehicle, or a total of 40 lbs of rotational weight removed from the vehicle.
So how much of a difference is this going to make? I don't know; well, at least not yet. But I do plan on performing back-to-back comparisons between the two sets and seeing just what I can come up with. Here's what tests I have planned so far:
0-60 MPH
60-0 stopping distance
100 mile combined city/hwy fuel mileage comparison
drag strip visit for 0-330'/600'/1000'/1320'.
While I can't guarantee that all my tests will take place under exactly identical conditions, I will make sure to have each test performed on the same day within a ~1-hour span from each other. Look for the results in the near future.

Once this is complete, then I will be scheduling a visit to the local lift to potentially install a full URD exhaust system, a Bullydog tuner, and a bespoke aluminum rear driveshaft. Once that's complete, I plan on running similar tests (sans braking) to see how much (if any) of a difference there is.

Again, would greatly appreciate some feedback from the community. i want to hear what you've done and what you plan on doing!

 

The transfer case on any actual truck is what the selector switch reads. When in two high you only have power to the rear wheels. When in 4hi you have normal gearing power but to the front wheels as well. In 4lo the gearing is lowered for better traction to all 4 wheels etc. As for your own build you just have to do what you please.

 

Prop shaft does not spin in 2WD, the front differential disconnects when the 4wd is not in use.

2007 did not have a Pro trim.

You have LSD if its a sport trim, which has advantages and disadvantages as well.