FPS drop during Descent

Hi all, lately I have been noticing that my FPS with the T7 drops once I begin the Descent phase of my flight, it espescially noticable if I use the Electronoc Checklist onboard. My normal FPS, even during take-off is about 12 FPS in the cockpit, this I find totally acceptable, but during landing and descent y FPS in the cockpit is 3-4, still bearable for this aircraft but its not easy to do a manual landing under shuch laggy conditions. I find it particularly odd that after securing the aircraft and shutting down the engines my FPS rating jumps back up to 12.

I have a windows 7, 64-bit system with a first generation i7 quad-core processor and four gigs of ram. My system is a little outdated but is still able to run the T7 at 12FPS with no noticable lag, which is all I ask for as a simmer. has any one else been having this type of frame rate drop.

Thx