Hi Steve, playing the Trumpet has been a source of frustration for thousands of people around the world …probably millions! I feel your pain and frustration. Believe me I’ve been there!!
The effort required to play with a great sound, extended range and endurance is minimal. Just watch the guys who can do it at the highest level. It’s effortless for them!! No harder than normal conversation! Rafael Mendez knew this 70 years ago!
Passive Reduction is with out a doubt one of the keys to playing trumpet efficiently. Taking enough air in is really important when practicing the singing C series. Really work on extending the amount of air you can inhale and then just relax and let the air do the work. When you take this approach you will slowly start to notice the muscles in the lips and face do the work (body is not engaged, just relaxed like a balloon deflating)
I highly recommend you revisit the singing C series and really take your time time with it. Never push if a note doesn’t sound, just relax and let the air do the work. Eventually as the weeks/months go by the notes will sound and become easier. Work on lip flexibilities starting from low C# to F# and only move up when they become effortless. Patience is the key to improving.
Wind Works is an amazing source of information for Trumpet players. Would highly recommend this website to anyone serious about playing the Trumpet!

Trumpet playing can be effortless if approached correctly and efficiently
Good Luck!