I just came across a user review for this pack and it seems they've found the same problem:
"It's advertized as being 3lbs 8oz for the medium. All three Meridians I weighed were 5oz or more heavier and they ALL weighted 3lbs 13oz for the medium."
That's exactly what I found. I wouldn't complain about an ounce or two, but 5oz over is pretty ridiculous. If I had known I may have bought a different pack (probably the latitude vapor).
I'm in Australia, so it's not really worth sending it back for an exchange. I'll probably just try and cut away extra straps etc to bring the weight down. If you're thinking of buying this pack -- be warned! It will probably be 5oz/150g heavier than specs.
I do like the pack though. It is surprisingly compact, but there is a ton of space if you loosen the straps and use the extension collar. Feels very comfortable and supportive.
I'm not sold on the lid which converts into a fanny pack ("bum bag" here in Australia). The lid itself is very handy, but the pack it converts into is kind of awkward because there are extra straps and things hanging off it. Plus the convertibility doesn't come for free... you're carrying an extra (small) belt around inside the top of the pack, and there's an extra hidden compartment to hide the belt! I'll probably cut off all that stuff because I can't see myself using it.
If I really want to cut down on the weight I can remove the lid altogether. I tried that this morning and it weighs around 1550g... not much under the listed weight with lid! I've read that removing the lid was meant to get you down to about 1350g. D'oh.
Oh, by the way, this "overweight" issue isn't related to sizing. The GG website gives different weights for the small, regular, and large versions of this pack.