Transfer case not engaging properly?

I'm having a problem with the vehicle listed above's transfer case halfway engaging into 4 hi. I could shift into neutral and hit 4hi then back to 2 to get it to undo at one point but when it started this week it didn't sound the same and thought it was the brakes till it started hi pitch whine. Because of what it did last time I drove it and other problems I've been having I'm wondering if it's all connected by electrical or vacuum. When it shifted this last time, the brake pedal dropped to the floor. Over the summer I had very hard brakes due to brake booster. Just didn't get around to fixing. That along with the overheating problem subsided as the temperatures went down in fall along with the hesitation during accelerating. Oh, and during the summer when the vehicle would start to overheat is when it would slip into 4 hi. Is there a vacuum hose that could have a light leak or problem that is connected to all and or computer or wire that could be causing sensor malfunction? Also is there any connection with the 4x4 system to the braking system that could cause the brakes to not release properly causing early wear of the pads and rotors?