I Walk Every Morning 3-5 Miles Thru My Development. When

I walk every morning 3-5 miles thru my development. When I go with the hiking club on Sat the hikes are moderate with elevation,when I hit the elevation my chest tightens up for 5 minutes,no hard pain,but a scary feeing. No shortness of breath other than the climb up. Then it goes away and I am fine the rest of the hike.
It only happens on the hikes and only the first elevation climb. I am 73 never been in a hospital and BP 125/75