Buddy, what ever you do for the shin splints, make sure you get it fixed quick. How tall are you? I'm only 5"3, had nothing but problems on ruck marches...ALWAYS! The pain would reach the point where I would loose feeling from my knees down. Ended up getting 2 operations on both sets of chins. The VAC call it "Exercise Induced Compartment Syndrome", the medical term is called "bi-lateral fasciotomy" Either way, they go in and cut out segments in the 'sack' that encases your shin and calf muscles so that they (the muscles) can expand while being exercised. In my case, that sack had gotten very thick over the years, the numbness I was feeling was from the lack of blood circulating properly into the shins and calves (very painful after only 3kms), made the ruck marches pure hell for me, made the BFTs even harder!
I do not recommend getting this procedure because on my first operation, permanent nerve damage was caused by the Dr. to the right leg on the inside of my ankle and 2 years later, put on a PCat and was medically released because I wasn't able to complete anymore BFTs, not operational, not employable! That was the policy!
My advice to you my friend, stay fit for as long as you can. Like the other troops have already said, ruck marches just suck, plain and simple. Switch off the brain to the pain, if you have too, take some pain killers before hand (if you take pain killers...if not, start taking them!) think of something else and it will be over before you know it.