Problem with long flights, my 747 slows down then stops

a. This was discussed at length when the Queen first came out. A search might find it.b. Set engine rating to CON to allow more excess thrust, to better deal with weather transients. PMDG did not agree with me on this at the time, but I feel their analysis wasn't accurate. Flight test has been my expertise before retiring, and still is.c. FSUIPC full version enables proper control of those transients, limit them to 1Kt/sec and 1 degree/sec wind velocity change. Even then you would see pressure changes coming in that drop the aircraft 100 ft in 1 second.Edit: I did not want to get you all into a detailed flight mechanics discussion, and therefore wrote just what to do with little reasoning.