Heavy Steering

Hello all:

I haven't driven the Mustang in a while. I charged up the battery and pumped up the tires, but when I took it out, the steering is very "heavy" as if I have a flat. Not so much when I'm at a standstill, but while driving. After a slow, tight turn, the wheel won't even return to center.

I, of course, checked the tires and the power steering fluid.

'87, 5.0LX, 5 speed, vert. http://www.paul-davis.com/mussy.html

Any ideas or suggestions?

Thanks.

Paul