My first question is, if it is too big for your gzip, how did you get your .gz in the first place? I suppose you got it off another system or something..

From a quick trip to the gzip homepage, FAQ #10 seems like it might be relevant, because it is about gzip handling files larger than 4 GB (it requires a patch to gzip and some added compliation flags for AIX, which caught my attention in your case). However, your file is nowhere near 4 GB. Skimming quickly though zlib's homepage, I could not find any thing about maximum file sizes for zlib. Gzip and zlib are both based on the same algorithm (deflate) but the file size thing might just be a soft limit set somewhere. My suggestion is to dig through the zlib page, and if you can't find anything there, email the authors of zlib.

Anyway I hope that helps a little :)