When Pynchon writes about Slothrop naked in a barn getting attacked by a witch's owl you can just laugh at it, you can just be disgusted by Captain Blicero, etc. No mystery solving required.
I think its status as "serious literature" does it a disservice in this regard. School teaches us that literature must be carefully scrutinized in order to not miss the obscured meaning packed into each and every passage. But treating Gravity's Rainbow with this level of scrutiny leads only to madness.
Funny enough GR does have a bunch of secret messages (Tyrone Slothrop -> Sloth Or Entropy), but they aren't why the book is good (closer to why the book is bad) and aren't necessary to enjoy it.
We aren't taught (in American schools, anyway) a lot of how to ingest these genres of media. Hence the refrains (about abstract art, e.g.) "my 5 year old could paint that!"