Frame Rate Problem-737 Series 2D Cockpit Only

I am still having trouble with FPS on 2D cockpit of all 737 series. No problems with 747-400,747-F, Level-D 767 or default FS9 planes. Rates drop from 30 to 8-9 in cockpit view. Sometimes immediately, sometimes after 30-45 seconds or so. If I pan or use any other view, rates are steady around 30 as they are in all other aircraft. Rates then jump wildly-back up to 30 and immediately down to 8-9-so a lot of stuttering.I can list my specs but since the 737 used to work, don't see how it's a hardware issue. Running an Nvidia 8800 and quadcore HP.I have deleted FS.config but no change either. Any thoughts?Thanks.Mark Kessinger