2007 Toyota Tundra - spark plugs

I have a 2007 Toyota Tundra with 140,000 miles. When should the spark plugs be changed? Also, it takes longer than it should to shift into 5th gear. How can I remedy this?

Spark plugs should have been changed 40K miles ago. If there is a delayed shift, I’d suggest you change the transmission fluid and filter as well.