Slow brake pedal. (slow to return to top)

[kensousa]

I have a '71 Cheyenne with factory power brakes.
They work just fine, but I've noticed that the brake lights stay on quite a while after taking my foot off of the pedal.
I've looked underneath at the brake light switch to see if it was slow, but since the plunger goes in to turn the brakes off, that's not really the issue.
When I take my foot off of the brakes, I can reach behind it with my toes and "help" it return all the way up and then the lights go out.
If I don't "help" the pedal back up, it might take 15 to 20 seconds or more before the brake lights go out by themselves.
Any ideas on what to look at to fix this?

thanks
KS