The real shuttle definitely gets higher than 7000m .... And that's my issue... it also is very unstable when launching (I tried to set up mechjeb with RCS on and off, with different settings, and also launch manually, nothing helps....). 7000m is max. AT around 5000m boosters go off, than it just increases altitude slowly, but at ca. 7000m i just can't get it pointed up, it flies horizontal and eventually starts to descend...
So the question is, is there anything special I need to set up to get it into orbit?