1998 2.2 weird cranking issue

I have a 98 S-10, 2.2 liter, 5 spd manual. Ever since I bought the truck in 2001, I have occasionally had a weird crank up. It sounds like the starter motor is just cranking slowly. Now, it has become more frequent and I am worried that I need to replace it. What could it be? Once the car starts up, it is perfectly fine and runs great. Just on startup, sometimes, it cranks really slow.

What do you think?
Thanks.

I've got a 97 that does that. I notice if i clean the crud off my poitive battery connection it goes away. But I've also been told it's the starter relay. If it keeps doing it after I do a top post conversion (side post suck ass) then I'll replace the starter.