Packs do wear out, which may be part of your problem. The big issue when we age is that we have to go to an inflatable pad (I just got a custom insulated air pad from Kooka Bay that's 3 1/2 inches thick), which doesn't add the load-carrying structure to a frameless pack that a closed cell foam pad does.

There are excellent framed packs of about 2 lbs. or less that will carry a load of 30 lbs. or a bit more. These come from "cottage" manufacturers, not from the mainline companies, and most are not carried in stores. You'll have to be prepared to pay return shipping if the pack doesn't work. These include ULA packs (I'm thinking especially of the Circuit), Six Moon Designs Starlite. Mountain Laurel Designs is planning to produce their Exodus in a framed version. The new Elemental Designs Aquilo has good reviews, and has been tested satisfactorily with up to a 30 lb. load. If my current pack falls apart, I'll definitely be looking at the Aquilo and the ULA Circuit first.

My current pack (the discontinued Six Moon Designs Comet) has carried up to 37 lbs. fairly comfortably, with the "optional" (mandatory, IMHO) stays. To be exact: my shoulders, back and hips were fine, but my knees and feet were screaming! No buckling (collapse of the torso) of the pack (good sign it's overloaded); the only thing that buckled were my knees, lol! The SMD Starlite is almost identical in design, but larger capacity.

The most important thing is how the pack fits you--with the load you plan to carry in it. Pack fit is almost as individual as shoe fit, so you'll need to do a lot of trying on, with your gear inside. When you get one home, hike around the house for several hours with fully loaded pack (your gear, equivalent in weight and bulk of a week's food, a couple liters of water). A very boring "hike," but this step allows you to test the pack while you can still return it.