You need to list your engine and trim level in order to look up the correct part. I looked up the 2013 Highlander V6 model on
www.rockauto.com and the Gates, Dayco, Continental, Ultra Power idler pulleys all show those two part numbers, so it appears they are interchangeable. To be sure I would look up your specific [year/make/model/engine/trim level] on several different parts sites, including Toyota OEM as you have done, to narrow it down.
For many vehicles, you cannot buy the tensioner pulley separately -- you must buy a new tensioner assembly. But sometimes the tensioner pulley and idler pulley are the same part, so you can try to get the pulley off the tensioner and replace it, *IF* you can find a good match. But if your vehicle has a lot of miles, you might want to just replace the tensioner assembly for peace of mind. My experience is the tensioner pulleys are very difficult to get off the spring arm because they are not intended to be replaced separately.
My vehicles are garage kept so the components tend to last a long time. If the bearing spins smoothly and everything looks/works good, I will carefully pull the grease seals and repack the bearings, done this many times without issue. But it *HAS* to be in good condition before I will bother repacking grease and reusing the pulley. Again, often the best course is to replace the assembly.
