Just Cause 3

Of the eight classes of gear mods, tethers are the easiest to unlock every gear mod for, as there are only 4 mods that require a total of 15 gears to unlock. This means you can get 4 gears in three separate Scrapyard Scrambles and 3 gears in the fourth Scrapyard Scramble to unlock this, which is very manageable.

The Scrapyard Scrambles are located:
1. Insula Fonte, Sirocco Nord: Seaport Scramble
2. Insula Dracon, Petra: Stockpile Scramble
3. Insula Striate, Prospere: Secunde Scramble
4. Insula Striate, Rocca Blau: Seismic Scramble

For these events, you have to tether a magnet behind your truck, then toggle LB to either magnetize and attract Bavarium or demagnetize and drop Bavarium into a sloped pit. I found it easiest to drag 10,000 points worth of Bavarium behind me before making my first deposit. This adds a minute to your timer and sends out the first wave of enemies, and I would climb on top of my vehicle and blow up the enemies before collecting another 10,000 worth of Bavarium. Repeat again until you pass 30,000 for each event. I drove slow and steady and had two at 5 gears and two at 4 gears on my first attempts. Getting the last 2 up to 5 gears took one replay apiece.

If you have the Bavarian Sea Heist expansion, once you unlock the boat invaders challenge, the Eden Spark is pretty easy to unlock every gear for. The eDEN Spark is the Hammer of Dawn like weapon that you get at the end of the dlc.

Once I ran through it once I had three gears, I exited the challenge screen, and applied those mods, and the second try I got 5 gears.

Trikke den 1e provides the values in his staying power solution:

- Transport Boat : 500
- Corvette : 1000
- Heavy Patrol Boat : 2000
- Light Patrol Boat : 3000
- Helicopter : 8000

Just wanted to let it be known that if you own the Expansion pass, you can get this easily doing either the Mech challenges (there's only two) or the Sky Fortress challenges. I unlocked this without even knowing it was an achievement in the middle of my Sky Fortress run.