Most people on here report that the 1.5” collars work for them. Some say it is slightly nose high. Some say it is “dead level”. I think that the measurements all depend on what you have in the bed and sometimes, how much fuel you are carrying! These trucks have VERY soft springs and I have seen conflicting info, regarding what collars actually get you “level”. Some people say just go with 1” in the front and be done...just seems like a lot of trouble to only get 1” more clearance in the front. I’ll get my 2.25” front and 1” rears installed next week. I figured, if I’m going through the trouble of ordering parts, making appointments, leaving work and dropping off the truck, I might as well just go a little bigger! 37’s shouldn’t be a problem, once my tires wear down and need to be replaced.
Best thing to do; Measure the center of your front fender to the ground and center of your rear fender to the ground. That will give you a good idea as to what it will take to get you “level”. Wait until you have at least 500-1000 miles on the truck, to make sure your suspension has had a chance to settle down some.