When online with VATSIM and using Weather Feature, Climb Cruise OAT's are way tooooo high. Turn off VATSIM weather and temps become normal. Noticed that I couldn't climb above about FL200. Performance very bad. Checked temp while using VATSIM weather and the temps were very high. Like 70's, that's plus 70F.I do NOT get this problem using FSX default aircraft and some other purchased aircraft.Problem with PMDG FSX aircraft -- 747 and MD11? Or is the problem with VATSIM or a combined issue?The only workaround so far is to fly with VATSIM weather off.Anybody else found this a problem?additional Info: FSX-sp2, Windows-7 Ultimate 32bit, Pent-QuadCore-4GBmemory nvidia PCI Express Video Bill Peterson ~ Gulf Shores,AL