Your problem is on modelling side. I see same huge shading gradients on your mesh too. And while normal map can theoretically counter-measure them in a perfectly "synced" workflow you would never get it looking perfectly right in actual game anyway . 8 bit normal map with compression just doesn't have enough precision for…
Done for the daily Spitpaint group on FB. Topic - 'Really,really big train' The brave young mouse and his new friend need to get home. As they find somewhere cosy and settle in for the long journey his friend surveys their mode of transport... ''This is a really, really big train...''