I traced my daughter's learning issues back to problems with vocabulary. It seems like between second and third and fourth and fifth there is a vocabulary jump. Not just new words on her list (like chlorophyll and chloroplast) but just in the language they use to write their books. There wasn't a big jump between third and fourth grade--weird!
I found that there were so many "everyday" words that she just didn't know. Working on those vocabulary words helped her a lot.
She also needed a lot of help SEEING the new concepts. It seems that in third grade they start introducing concepts more. Second grade is more "what you see is what is there." My daughter needed help visualizing the concepts. I don't know how we ever learned without the internet! I'm constantly googling pictures of things for her.
If your daughter is only in 3rd grade, 3 hours on one day of tutoring seems like a lot! If I were you, I'd invest in a tutor that maybe does an hour a day, maybe a high school or college student that is willing to help her with her homework. That way you could take care of your other children and know that your daughter is getting help.