Is there a maximum files size limit to the autobackup plugin?

I've used the autobackup plugin for years...love it and love the updates to it that enabled basically a full site backup. No problems until recently and I "think" the fix may be a simple series of upgrades...which I have NOT done yet but wanted to get clarity on the issue first.  This particular site is still using CMSUltima v3.75 (Build 2818) with autobackup plugin v1.04.  The plugin times out and I'm guessing it's probably a resource issue as the combined website files are a little over 4Gb (two of the pdf files are nearly a gig each). Does this sound correct that it's just too much?