Resting pulse 88 walking 2.7 mph pulse 53?

Seems odd: You probably know that heart race increases with exercise, including brisk walking. If you're very athletic, leisurely might not increase the pulse at all but it wouldn't likely drop. In my practice, when I get an unexpected finding like this, I check to be sure I'm measuring correctly. Try checking it right after your walk when you're sitting down & can get an accurate reading.