The stress is over issues that the client is pressuring us to solve before a deadline, that usually requires overtime. I always refuse to do overtime, and try to work less rather than more. This creates a situation where my colleagues resent me because it feels like I'm not doing my share since they roll over and do whatever it takes to meet the deadline. And the client never learns, expecting overtime.
As a result, my last performance review wasn't great because my employer would prefer that I worked as much or more than my colleagues while only paying me 40h (clients are billed by the week, not by the hour.) I'm not in the top performers at my job either, I'd say I'm average at best. I don't feel like my bargaining position is particularly strong at the moment with this employer, and I negotiated my initial salary well from what I gather from colleagues I've discussed comp with.