I've been doing training hikes with my new Osprey Exos 58 in preparation for a SOBO thru-hike of the AT. I have been carrying a 15 lb. load. I find the pack most comfortable when the straps are fairly snug. When I go for a 1 1/2 to 2 hour hike I find myself retightening the shoulder straps and waist belt 3-4 times. Is this normal? Should I just get used to it? Is there something I can do to reduce the "slip" of the straps?