We are at around 4800 ft above sea level.
I'd check the temperature of the oven with a separate oven thermometer. It might just be your oven is a bit cool. I live above 7000 feet and never really have to change my cooking times for meat.
Baking and boiling an egg are much different at higher altitudes. Most cook books are based on sea level cooking. Roasting etc are the same at any altitude as it is the temp that matters not the altitude.
Having lived and cooked from 5000 ft to 11,000 ft elevation, the short answer is YES . Really amazed how I had to shift cooking times, including boiling water, at sea level where I now live. Takes less time. And as you know baking has its own unique criteria that must be met at high altitude. Takes longer to reach heat at alititude.
The first time I made Thanksgiving at 8000 feet, we ate really late!
Yes the cooking process does take longer. I know if you google it there may be a cooking elevation chart.