1 It sounds like you're working for Wal*Mart.

2 A year with a chopping block in view of your workstation? Ugggh. That kind of stress level would destroy me.

3 Hang in there.  I know you're trying, but it sounds like this company is particularly unforgiving and breeds burnout.  Sometimes this is God's way of telling you it's time to look elsewhere. I know that can be a challenge in this environment, but you should definitely be keeping your options open.  Your long time at your last job would show a potential employer that you don't just hop jobs and your time in this one will show that your making an effort.  It's also far easier to move to another job while your still employed these days.  Sticking around waiting for the ax to fall is not particularly healthy.

4 That one year of "probation" sounds quite long. Got the resume machine cranked up and placing them in places where you would like to work?
One can be picky about where, until you can't. 

5 Some managers are like that. They figure they can get more out of you with threats than with praise, while helping to keep salaries down (after all, you probably don't expect a fat raise if they're on the verge of kicking you out the front door...)

Really there's only three questions. Are their expectations reasonable? That is, are they setting a performance standard that's doable and which is a goal that you ought to be able to attain, or are they taking their 90% performance level and saying "yeah, this is average" to talk people down (or, worse, taking their goal of "we have X business to do and Y people to do it, so the standard is X/Y")? If they're asking for a level of performance that is beyond what they ought to expect, then it's time to decide to get out now, because you're not going to make them happy no matter what; they'll just hammer you for as long as you'll let them, and once they've thoroughly wrung you out, they'll just toss you aside.

Second, how about your own circumstances? If they're asking for a reasonable standard but you're just havin' trouble getting it done, well, that happens; none of us are good at everything and some things just don't click for some people.

Finally, if you think they're asking for reasonable performance, and you think that performance is within your capabilities, is it something you're going to be happy doing for a while? If you're needing to work lots of overtime and trying to hit their targets is going to leave you a wreck, bugger whether it's possible, you've gotta decide if it's what you want to be doing to begin with.

You don't have to bail immediately, but if you decide that you need to find some other place, go find one; don't tie your self-esteem to someone who's willing to damage it for their own business purposes. Stick with these guys until you land something else, then take off; they've made it clear they have no loyalty to you, so feel free to return the favor.