You guys got the whole hi/low range thing backwards. Think about it: dropping it into a lower gear makes it easier for the engine to move the truck. The best possible setting would be 4th or 5th gear, hi range, 4wd. Hardest for the engine to turn the wheels/easiest for the wheels to keep the engine stationary.

4th gear and a 24 inch breaker bar were all we needed to get the crank bolt off my friend's 89 2WD with 278k.

My Truck: 1987 XtraCab DLX 22R 4WD 5 Speed Manual
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"Speed has never killed anyone. Suddenly becoming stationary, that's what gets you." -Jeremy Clarkson