What is
$resp? It sounds almost like the download is occurring above the code you pasted, and that
$resp is an object holding the results (with the full content of that result). Depending upon the level of abstraction this object is providing you, it may not be possible to do what you're trying to do while still using it. In order to get this kind of progress, you'd need to be inserting progress-checking code directly into the read loop, updating progress information after every block received (or less often). Unless whatever module you're using allows you to hook into that, you'll have to break that out into code you write yourself to retrieve the data. To help further we'd need to know what you're using to retrieve the data.
Or are you talking about getting progress information while saving $resp->content into the DOWNLOAD filehandle?