When I went shopping for new rims and tires for my 12 Ram 2500 CTD I found out some interesting things. Like mentioned some of the nicer looking rims aren't strong enough. I went to Discount Tire and worked with one of the sales guys. He got out a book and we both looked thru for some rims. I was going from 245/70/17 to 275/65/18. I found a few rims I liked and had already told him I tow a 5th wheel. On every rim I was interested in he called the rim MFG and asked about towing with them. One MFG actually said no if I was towing a 5th wheel. Long story short I finally found some that worked. So even though the rim has the load rating it's possible it may not be recommended for 5th wheel towing.
Sad but true story, I went to Les Schwab before and briefly talked about rims and tires. Some don't have load rating info on them so when I asked the LS sales guy he said don't worry about it, that if they have 8 lugs then they'll be fine. So not true.