Some basic help needed

I just purchased the beautiful PMDG 737 (SU2) last week and have spent 5 or 6 sessions practicing. So far, I have been unable to get her airborne and stable at cruise level. I have followed the tutorial by Timothy Metzinger meticulously (I think) and have no problem with all the pre flight, engine start, etc.. I have previously used the PIC 767, Dreamfleet 737 and PSS 747 successfully. I am beginning to wonder if I have a problem with my install..or am I brain dead?!?! For example, I set the initial altitude at 5,000, get airborne following the PFD/FD climb angle, then turn on AP, increase the speed to 250 knots and she just keeps climbing past 5,000 and never getting up to speed. My pitch angle seems to be way to high and I stall out. I have the trim set according to the FMC at 5.5. I am probably missing something obvious. I would appreciate any help. Thanks,Steve Canham