If you go to a 37" tire, PLAN on LOTS of problems. Even a 35" tire is still something I would not attempt on a ranger with IFS. Weakest point of ANY IFS system is the Tie rods. 33" are plenty big for IFS. Most 6 inch lift kits I install dont run a tire bigger than 34" tall and no wider than 12.50". With the Ranger and Explorer front ends I see SOOO many Issues with all the front end components completely stock. Add a bigger tire and it will just add to how much money and time and parts you put into your truck to keep it mobile.
RCD is a great company and Ive never had a single issue with their kits, Ive installed close to 20 kits in the last 3-4 years on various vehicles, most being GM 2500HD trucks DirtyMax style.
Just Be Aware of what Can possibly happen after a lift kit and big tires. Me personally, being in the field of work Im in, would not run a tire bigger than 33" on a Ranger The front end will not handle it comfortably and hold up.