As someone who drives the S79 everyday, I can tell you that the hybrids struggle to get over the bridge. It has nothing to do with the governor, as that is set at 45mph. Some hybrids can barely maintain 30mph over the bridge when loaded.
I've actually had the entire bus shut off while I was climbing the bridge and had to coast it down to the Brooklyn side and wait for a tow.
If I were in charge of Yukon, I would put the hybrids on straight local, and take some Novas and put them on the SBS.