91 200tq-what to look for?

[Mikea2769 at aol.com]

Will be checking the above in a few days. I'm familiar with the "normal" 
things to check on a used vehicle and have kept an 87 5000cstq running to it's 
present 302k miles, so am familiar with many "quirks" of this model. Anyone care 
to comment?
Also-how does one check that the diff locks are functioning on the 91 model?

Thanks,
Mike Aiello
87 5kcstq, 302k miles. orig. owner