[Q] Super slow file transfers over USB topic

I only use the internal memory on my Rezound, not a removable micro-SD card. Prior to rooting and installing a custom ROM, copying large files to the phone by USB was pretty quick. That was with ICS and I understand that since Android 4.2.2 you can only connect by MTP or mass storage mode. But now copying files TO the internal storage is extremely slow (about 1.4 MB/second). It's not the cable itself, as copying files FROM the internal storage to the computer goes quick, like it used to. Could the internal memory be formatted improperly? The drivers for the phone on my Win 7 computer (64 bit) looked like generic Microsoft USB drivers, but when I tried to update with drivers made available with the HTC Sync app, Windows didn't allow it, saying the drivers it was using were the most current. Copying from the computer to other USB devices like flash memory sticks is quick and fine, like always. Thanks for any help.