3/8" cable with a load of 3,000 lbs.?? I just hope the WLL is 5 to 1 but I still wouldn't use it for a couple of reasons.
1. Its too hard to work with.
2. There are better/safer things to use.

I got a 50ft extension made when I got my winch rope made. Its rated for 20,400 lbs. That and the winch cable (100ft.) and if neccessary, my strap (30ft/30,000 lb rated) and I think I'm good to go. (180ft total)
Just my opinion.

If you are still set on using this cable....Try a marine outfitter or fishing supply, they make up rigging all the time and are set up to make proper connections, and will have what is necc.

Kary