Latitude E6400 fan issue, laptop slowing down when docked

I've had my Latitude E6400 for about 3 1/2 years now (bought it when they came out in fall 2008), and I've constantly had issues with the laptop overheating (fan runs constantly) when docked (in my desktop environment). Lately the laptop has been slowing down to be nearly unuseable. But when I undock it, the problem typically goes away, although not always. This has been very frustrating. I believe that I've had Dell replace the fan at least once a couple years ago, but the problem is still here. Any ideas on a solution?

I'm running Windows 7 Ultimate 32 bit with 4 GB ram. I'd like to upgrade to 64 bit.

 

I think you are looking at the "classic" E6400 throttling issue. Take a look at Throttlestop and see if it helps. Try the latest BIOS as well, if you haven't either.

 

Which bios are you running?

 

Monitor CPU and GPU temperatures.
If it has the nvidia GPU, there's a possibility of contact (non-contact) issue with the heatsink and the GPU.