Some further info here. I have put the adapter and the router (DIR-655) into B mode only and that does resolve the problem, but limits my downloads to about 5.5 mbps. I read in one post somewhere that maybe this could be related to a "turboboost" mode set up that the router may support and that the adapter doesn't support. I don't see any turboboost for this router on any of its setup pages but I could be missing it. Anyone know if this could be the issue?
