I'm using vim for LaTeX and I'm using latex-suite. It gives me nice syntax highlighting and folding, but in large files syntax highlighting gets "confused". If I open all folds, the syntax highlighting turns OK. I would like it to "just work" all the time though.
I seem to recall an option that would increase the number of lines that is used as basis for determining syntax highlighting but I cant find it.
I don't edit LaTeX, but perhaps you want ":syn sync fromstart"? Just be warned that this can significantly slow down Vim since it forces Vim to do syntax highlighting parsing for the whole file rather than a section of the file. See ::help :syn-sync".