Mark Twain is of course a master of satire and so it is fitting that perhaps his greatest novel should be used to satirise a number of things. However, the chapters you have identified chart what is known as "the evasion", or the period when Huck Finn and Tom Sawyer get back together and hatch an incredibly elaborate plot to free Jim. All evidence of the thoughtful, maturing and developing Huck is gone in these chapters, some critics argue.
However, I think it is clear that Twain is satirising romanticism through the character of Tom Sawyer. It is clear in these Chapters that Tom Sawyer envisions himself as a romantic, almost mythic hero. For Tom, hatching an elaborate scheme is far more important than being honest with his friend and telling him about Jim's release. Consider what Tom says about Huck's practical and straightforward plan in Chapter 34:
"Work? Why, cert'nly it would work, like rats a-fighting. But it's too blame' simple; there ain't nothing to it. What's the good of a plan that ain't no more trouble than that? It's as mild as goose-milk. Why, Huck, it wouldn't make no more talk than breaking into a soap factory."
It is this desire to have an incredibly exciting and romantic plan, fraught with danger and worry, that drives Tom Sawyer to concoct his ridiculous escape plan, that even Jim has to play a part in to help them out.
This is one of the central aspects that Twain is satirising in these last few chapters - the romantic notions of Tom Sawyer clearly show the absurd lengths to which he is prepared to go to have a "proper" adventure and achieve a "real" feat.