Yeah, if you're blowing a hose off the top of the valve cover, that sounds like a breather hose, which indicates a breathing problem and/or excessive blowby. Certainly with a rebuilt engine, not broken in, you'll have more blowby till the rings seat. I had problems on two engines after rebuilds not breathing properly, and blowing oil out seals... in one case, a breather element was blocked, in the other on my IT car, the hose was there, but was bent in such a way as to kink and block the breathing - DOH!

So I'd suspect you have a breathing problem, from what you describe...