OS X :: Mac To UNIX FTP Server - Cannot Upload Files

Two months ago I switched web hosting providers/services from a Linux server to a UNIX server. For the most part the functionality is fine but the ability to upload files using any FTP client is near impossible. We've tried Fetch (4.x and 5.x) Filezilla, Cyberduck, Dreamweaver, and an old copy of GoLive but it takes 6 minutes or more to upload a 230byte file!. The upload is relatively fast but it hangs up on the exiting handshake, or drops the connection and has to reconnect.

We spoke with Fetch and tested both copies on their UNIX server---no problem. We've tried our other clients on other UNIX, Windows, and Linux servers---no problem. We've had the web host and our service provider look at DNS blocks, etc. and all seems to be fine. Pings and trace routes seem fine. The web host company indicated that they believed that it was an issue with their server but eventually threw up their hands and said that they couldn't figure it out (not Mac friendly I suspect). My questions is two fold:

1) Can anyone give me an idea what IS the problem?
2) Can anyone recommend a good 'Mac-friendly' web hosting service that doesn't have issues with Mac's, will allow installation of a variety of CMS, eCommerce solutions, and of course seamless FTP access with variety of clients.