What's the reserve on the battery? I'd look at upgrading the alternator to a later OEM unit. There is a list in the FAQ I believe.
Also, are you reeling out all of the cable or just the first couple wraps? If it's just the first few wraps, you need to unspool a lot more cable. Double line it if you have to. With each additional wral the winch looses strength. So, you could be stressing the winch unecessarily.