How much Larry McMurtry is too much? Ready or not, here he comes again with the third installment of his seriocomic Berrybender Narratives a scant six months after book two. By Sorrow’s River (Simon & Schuster) won’t win him another Pulitzer, but the pages blow by like a prairie wind in this 1830’s-era yarn about taciturn trappers and hedonistic Brits braving Indian territory for the sake of adventure in the New World.