I think you are correct that the electric winches are not made for that. My brother burned out a couple on the front of his gator, pulling logs and using it for "work." They were Warn, but I'm not aware of any that have much of a duty cycle. It takes a bit of online investigative work to determine that even the "hottest new" winches are not made for much hard work because they require VERY long cool down times before you can work them again. The harder the work, the shorter the duty cycle and the longer the recovery phase.
If you can't find a hydraulic winch, maybe you can find a portable gas powered winch you can mount in the bed and do what you want.
Good luck