G'day,
First, sack your mechanic(s) - if this problem is still existing after they claim to have replaced the brakes then they are sadly lacking in mechanical ability.
Tip: do NOT drive far on hard surfaces in 4WD.
1. Double-check that 4WD is NOT engaged and that the transfer selector is in 2HI.
2. If you have manual hubs on the front, check that they are in the 'Free' position.
3. Jack up the passenger front and check the wheel for free rotation and wiggle it to check for 'slop' in the bearings.
4. Get someone to apply the brake while you rotate the wheel - does it lock and then release OK?
Come back after and tell us the results.