Advice for us 5.7-6.0

Holy hell am I suffering right now. Most of the time I’m getting up tiered and having to fight against German and Soviet heavy’s like the tiger panthers king tiger and the IS variants. But the American cannons are just too weak don’t argue with me that I’m not flanking correctly because I have side and back shot them with the 75-76 ml. And it won’t even pen I have no idea I’m only able to kill the lighter tanks/ the aa