I wouldn't be getting rid just yet, my big brindle dog was rehomed as he was a complete winge and 'wouldn't' pull big game, he was ran doubled up at deer, on his own at deer and never wanted to know!!! This dog was always very puppyish and when the lad who had him, could no longer keep him, i decided i'd take him back and jsut keep him as a pet if need be, but in the week following his 3rd birthday everything just clicked, and he's now pulling stuff without probs and looks like he's been doing it all his life!!!! Most likely a late maturing dog for me, hopefully it'll be the same for you too!!