I have towed boats, toy haulers and my fifth wheel trailer on the 60 for at least 40 years, most recently in November last year on my way back to OC.
Yes, it's twisty in spots, a few ups and downs, some speeders that think they can drive, lots of semi's. Never been an issue for us. Choke point is returning on the 215 as it feeds the 91, has always been this way. Bumper to bumper for that stretch, even though they improved the interchange at the 91.
I you are not used to this type of road, now is a good time to get comfortable driving it. Don't go during rush hour traffic, stay to the right and relax. Not all roads are straight and flat.
My 2 cents.