Here is a coyote at 400mm uncropped, at something like 130 feet. I used f9.5, 1/500, ISO 400 in pretty good light.
Wolves are bigger so you could be farther away. So 400mm is probably OK, 500mm would be better. This was a manual focus lens and represents just about the minimum quality, focal length and price that would be an improvement over the DA 55-300, probably $300 or so. An older autofocus Tokina or Sigma are probably better, and maybe $600. Prices are just a guess, and since these lenses are all used and old, condition and availability can change that a lot.
Try cropping your best 300mm shot by 50%. When you're taking the shot, plan ahead to crop by keeping the exposure correct for the part of the image you'll keep. The camera will set exposure based on the whole frame, which may throw off the exposure for the wolf.