I've seen a variety of threads with all sorts of answers that relate to my problem, but nothing concrete for my situation. Help please! :)

My info:
Zen Cart 1.3.6 Database Patch 1.3.7
(will be doing a fresh install next month hopefully, but need to get this working in the meantime)
Linux 2.6.9
Suexec host
PHP 5.2.6 (Zend 2.2.0)
MYSQL 5.0.51a
HTTP Server Apache 2.2.9 (Unix)

Attributes:
Redirect TRUE
Streaming FALSE

Other (new host has been great at changing these as needed):
max_execution_time 180
php memory limit 512M

The situation:
We moved hosts (more details here if interested: http://www.zen-cart.com/forum/showthread.php?t=104641) and we have been having a problem with our pdf downloads. The previous host used FreeBSD and I "believe" we had downloads set to streaming, but couldn't really tell you because they had me locked out of this part of my admin, but by the way they worked I think this would have been called streaming. With the new server, I have it set to redirect. I prefer this method, but I'm wondering why it's not working properly.

The problems:
Some customers (like 1 in 5) are getting errors when downloading our pdf files (corrupt file errors although I know they are not). At first, the host started raising the max_execution and php memory. This alleviated the problems for some customers, but not all of them. Tonight a customer sent me the link from the pdf file she was trying to download and it had an .html attached to the end of it. She was on a Mac, but most of the others have been using Windows. No one has reported that they are on dial-up. The host and I cannot reproduce any of these errors, so this is making things difficult. Our files range from 2-60 MB and I believe it's mostly the larger files, but it appears that once a problem starts, it continues for all their downloads (this isn't definite though - I've had so many emails they're all a blur).

I can switch everything back to streaming I guess (not sure what, if any, errors we'll get that way). I'm just wondering if there's a solution someone knows of for our redirect or if there's a bigger problem here than I'm aware of. I have my pub folder set to 755 because we have a Suexec host (whatever that means) because that's the info I found in the tutorial for redirect vs. streaming. I tried switching it to 777 to see what would happen and found the download behaves differently for different computers. Some will get the pop-up that asks you to either save/open and others go straight to downloading the file (with the symlink?). Still though, those that were getting errors, still got errors. Sometimes it has helped for them to clear their cache after getting an error. Too many customers with too many situations to tell you if that's even worth mentioning.

I'm not very techie, but I'm trying to learn all of this lingo and my new host has been awesome to work with. I'm going through all of the steps for a fresh install but it's nowhere near ready. If you read the link above to our situation, you'll see that we cannot trust our system to upgrade. My prior host/developer/designer told me to not come here for advice because they had "improved" upon the cart. Knowing what I do now, these "improvements" scare me. So I'm wondering what "improvements" they've made that could possibly be causing this glitch. Maybe it's totally unrelated. Can you use redirect with FreeBSD? I know when I asked the former host about using the redirect method, they said I could not. Maybe they have something set to not work correctly with redirect?

Any comments/suggestions? Right now, all I can think to do is switch to streaming. It's a shame though when redirect works for most customers. I just would like to know why the redirect is working for most, but not all customers.