Jack up the front so both wheels are clear. Check if both wheels turn freely. If a brake caliper is binding and you have an 'open' diff, then when you turn the drive shaft by hand (hubs engaged) the axles will display the symtoms you describe.
If both wheels turn freely then turn one (hubs engaged, 4wd engaged) and note the result at the other one. An open diff will make the other wheel turn in the opposite direction and a LSD will make it very difficult to turn the wheel at all. Anything else means you have diff problems. If the hubs were the problem you would still see both axles turning. Hope this helps.
Cheers

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