Just tried plugging in a calculation also. I agree with Sue that you probably should have run the whole thing with 10ga but you might still be OK. Running 12ga for entire run, I figured you would have about a 7.4% voltage drop at 575ft. Suggested drop would be 5% or less though according to the calculator I used.
Just a thought, where you changed over from 10ga to 12ga, are you sure that connection is good and you aren't dumping electric there? (I'm not an electrician, just familliar enough to get zapped a few times here and there and do some hillbilly fixes round the place...)
