Hi Rich, congradulations on the new guitar.

It is a funny thing that I am guilty of as well. I find myself tightening up more so with playing rhythm than doing solo work. I think this may be because rhythm is so important and I need to focus on keeping those chord changes in time, whereas when I am jamming over a backing track I can just make stuff up and if feel much more relaxed.

Not sure if that helped you but that is the way it is for me.