Can you select MPE Hardware Acceleration in your General Properties?
Bill, I can't seem to find that...It appears that my Premier Pro is using it, but I'm not so sure about AE.
A knowledgeable member said previously that AE uses Open GL for Hardware Accelaration and not hte MPE
See this page for an explanation of what the Mercury Playback Engine is, including a statement that it has nothing to do with After Effects.
The setting that determines whether you are using the CUDA acceleration features of the Mercury Playback Engine in Premiere Pro is a project setting. Choose Project > Project Settings > General. In the Video Rendering And Playback section, select the appropriate renderer: Mercury Playback Engine GPU Acceleration or Mercury Playback Engine Software Only.
Project > Project Settings > General
That's where you'll find the "Video Rendering and Playback" option for MPE
After Effects does not use MPE, but does use OpenGL with the video card for certain renderings.
If you are unable to select hardware MPE in PPro (or if rendering is still sluggish), then It's possible you have a bad driver from NVIDIA. There are a few duds floating around right now and you can search for "driver update" in these forums for more information about that.