I am having the same problem and I host with BlueHost.
I tried to add
AddType x-mapp-php5 .php
to my root WP .htaccess file, but core upgrade blew up. I clicked it and all the PHP code spilled over the screen. It was quite scary. PHP code in a browser is so unexpected, I at first thought I broke something in the browser.
If anyone knows why the upgrade hangs at the download in BlueHost please let me know.
