5th gear is best. 1st gear makes it really easy to overcome the vehicle's brakes.
Only problem I have run into is either the brakes slip (engine off so no power boost), or the clutch slips. If the brakes slip get a stronger helper, stick it in 4wd and use the parking brake in addition to the brakes.
If the clutch slips you need to find another way to pull the nut off. Maybe the starter bump method? I used that a few times and once it worked and another time it didn't.
Then maybe homemade tool to keep motor from turning.