II Kings- It is a possibility the entire exhaust itself is resonating at the frequency the chassis produces at those speeds. The "pieces" they are talking about adding to the exhaust may be weights or hangers with dampers on them to change the frequency that cause the exhaust to "sing". I know we're talking about Chrysler here, but I am holding optimism that all will be well with this well engineered transmission built by my friends in Kokomo Indiana.