I just read every post here and it becomes clear how so many people get confused when reading through the different responses on a forum.
The op stated that his stock tires or 265/70/17 and right away someone stated that stock tires or 275/60R20, this was also backed up by another post......All Rams do not have the same size tire, my Ram also has 17" wheels and the stock tire size is 265/70/17.
Now people are having a discussion/disagreement about how to read tire sizes....more confusion and no help to the op.
I'll admit that I don't know for sure what the biggest tire you can put on your truck but I do know a 275/70/17 will fit, they will be close to 2 inches taller and very close to the same width. I used the terms "close to" because the actual size can differ from one tire brand to the next even if they are labeled as the same size, it won' be much of a difference but some.
is correct and tire rack is a great place to learn about tires, check out the link and it explains what the numbers mean.