I thought a couple of guys have put 37x12.50 on stock 20's and it was fine with the leveling kit...... maybe not.
I have the 37" trail grapplers and I love them. I have almost 40k on them and I would say they are a little less than half worn. I do a bunch of highway driving, I am very easy on the tires and MOST importantly I rotate them every 5k.
The only down size is that they are heavy compared to other 37's. They put a pretty big dent in my performance and MPG's....... But they are lasting a really long time which is a big deal when you are talking about a 400+ dollar tire.