The cubic polynomials $p(x)$ and $q(x)$ satisfy the following conditions:  
1. $p(1) = q(2)$  
2. $p(3) = q(4)$  
3. $p(5) = q(6)$  
4. $p(7) = q(8) + 13$  

Find $p(9) - q(10)$.

Let's think step by step and output the final answer within \boxed{}.
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