Morning Frank and welcome to this forum, nice introduction.
Great to hear your success with cheese and with book writing, nice website! Looking for forward to your input and ideas as I'm like Tea and learning lots and having fun. Have fun with building your cheese cave, the one I've set up is using an old freezer and so far here in Houston in summer I'm having the opposite problem to most people, too much humidity!
I'm not sure that elevation would change the rennet's action, could be milk in your area is different to others. When I used liquid vegetarian rennet I needed about 25% extra with store bought pasteurized cow's milk, with the powdered CHR Hansen rennet I use about 50-75% extra over recipe or manufacturers directions. Are you using Calcium Chloride on your store bought pasteurized cow's milk? Which from what I have read, it is even more critical when using goat's milk. Also, I've found that as rennet is such concentrated stuff, I need to ensure maximum dilution, which means initially stirring in 1/2 cup water, then trickle into the milk while stirring with a whisk, otherwise poor set. Just my 2 cents.