Payoff, I had crashed dived so perhaps that was the problem. I have played numerous careers & crashed dive numerous times during those careers & that was the first time I had ever experienced that sinking feeling.
I hadn't heard of the 'crash dive blues' before & the only change in my configuration was the installation of the GW mod. I had assumed (i know, i know what assume spells lol!) that it was something to do with the 'Hummingbird' mod being included into GW. I know GW & NYGM are different but GW uses the NYGM damage mod.
Anyways now I know to have a good helmsman, which I try to do, and not to crash dive then change depth.
Great community here & appreciate the help. Excellent mods for a game I spend way too much time on lol. I noticed this post was moved as well, sorry moderators for making extra work for you