Last month I bought 12000 lb viper brand(Amazon) winch for my 99 2500 4x4 Suburban it’s over 7000 lbs.I believe they recommend 1 1/2 times the weight of towed/winched vehicle, as a minimum. 6000 lb truck 9000 lb winch.
Just remember that the maximum pull weight (12k on that winch) is only available at the first layer of cable. As the cables stack on top of each other they change the overall drive ratio, reducing max pull weight. Moreover, there's a big difference winching up an incline...in soft conditions.
Hence the 1.5x recommendation.
