Shock questions

[kevinr1970]

Maybe stupid question here, but...
I have a set of four Rancho what I believe are RSX9000 shocks on my parts truck. This truck has a single front shock set-up. I was told they have less than 10,000 miles on them but the truck sat for about four years so they have about 6-8 years on them.
When I try to compress the shocks by hand it is very difficult. Once I get them to the bottom they return to full extension by themselves in about 30 seconds.

On my good truck I have a set of Rancho what I believe are RS5000 shocks. This truck has the factory quad-shock set-up. I bought these shocks in around Octoer 2004. They have about 6,000 miles on them.
When I compress them by hand it is relatively easy. Once they are to the bottom they do not return by themselves, even over night. I can extend them by hand with slightly more effort than compressing them.

My question is which one of these sets of shocks are working properly or are they both?
Can I install the a single front shock in place of a quad shock or is it too different?

The parts truck had a 2" lift (which is migrating its way to the good truck) but the shocks in the front are about 1-2" shorter than the ones on the good truck at stock height? Is this beacuse of differences with the quad-shock set-up?