This is very simple to do using QGIS using the OSGEO4W shell.
Simply open the OSGEO4W shell and run the following command line
gdal_translate -a_nodata 0 -of KMLSUPEROVERLAY -co FORMAT=PNG INPUTFILENAME.tif OUtputfilename.kmz
I've also had great luck exporting a raster layer from an .mxd to kml / kmz using the custom tool found here (I didn't create this or know who did): wankoelias / MapToGarminCustomMap — Bitbucket
It seems to do a good job of preserving raster resolution in the output, and can be ran straight from ArcCatalog inside of an ArcMap session. Just download and unpack the tool / toolbox locally, navigate to it in Catalog and give it a shot. Hope this helps!
-Rex