35's, 37's, etc... is talking about the total height of the tire, i.e. 35 inches, 37 inches.
There there is all that info on wheels, i.e., 17", 18", 20", etc...which is the diameter of the rim, you have backspacing and offset to determine, etc...
Going to taller, wider wheels & tires adds more unsprung weight at the 4 corners of the vehicle. That can negatively affect your truck's performance off the line, affect fuel mileage and accelerate wear on OEM suspension components.
Having said all that you can still upside, to a plus 1 or plus 2 configuration, without too much negative affect.
I really like the idea of going to a reputable tire shop in your area to discuss your options. Of course, you need to be a bit informed about the subject as it is your truck and they will be your tires and wheels you are running when you upgrade.
Here is a good link to start reading about tires and wheels:
http://www.ramforum.com/f41/wheel_tire_faq-266/
When you change tire sizes, you will experience some speedometer error. Indicated speed may not be your actual speed.
So, if you are curious about how big of a change you will experience, go here:
http://www.csgnetwork.com/speedocalibcalc.html
Here's a great thread populated with questions and answers from members here on their specific fitments. It's long but well worth the read:
http://www.ramforum.com/f40/guide_leveling_wheel_tire_sizing_06_4wd_ram_1500s-70918/
Good luck with your tire & wheel upgrade!