@puggles thanks for the files. As you don’t have a power meter outside, I am limited on the feedback I can provide. Also, how to you pace yourself outside - do you go by “feel”?
If you continue to train with a power meter, as you have been doing in Zwift, and you have a power meter outdoors, you will learn the power/cadence combos that work for you and be able to use that data to pace yourself outdoors.
So based on cadence and speed data only, I noticed that you lose momentum by spinning at high cadence then dropping it significantly, over and over, such that it has many ups and downs. Every time you stop pedaling and have to restart, you need to use more energy, and that adds up. In addition, often times you use very high cadence up the hills (95, 100+ rpms) and could be loosing speed that way.
Here is a screen shot of one of the sections of your ride. The yellow line is cadence. Note the big ups and downs.
To carry momentum, you need to change cadence but not have these big variations or stop. Carry momentum over the top and continue pedaling on the downhills. Shifting is also critical. Here is an example of keeping momentum going by always pedaling even though terrain and power vary quite a bit (blue line is cadence):
To efficiently maintain speed you need to “surf the terrain” and the way to learn that is first and foremost, do the workouts outside of ERG, so you can better work on controlling your power and cadence.
Lastly, are the riders in your group much stronger than you? Another consideration when trying to keep up with them is also developing strength.