Hi. My 1989 Ovation has a severe miss from midrange and up. I have cleaned the carburetor, replaced jets, spark plugs, fuel filters, and checked pipe for obstruction. If you stop or remain at slow speed it runs fine. It starts and idles perfectly. The severe miss and bog appears to be at the same RPM every time. Does anybody have any suggestions or previous experience with a problem like this? I would appreciate any help.