It's hard to say whether or not your springs are bad or not. I've refurbished old stuff before requiring these and have come to summation... they do wear out over time and if they're used alot. If they're not doing their job they're either bad springs, or over loaded.
I deal with something much older in my 92 model but it sounds as if the gas springs are the same specs used in both of our campers. I did measurements about a week and a half ago having the same problems you're facing. I have 2 springs, one the head end and one on the foot end of my bed with the lift coming from the side of the bed. My measurements for the springs were a fully extended 20.5" with a 6" stroke. I'm not positive of the exact reference point to measure and just wanted a rough estimate.
Currently, if the bed is without linens the springs do their job and hold the matress and lid up, with the bed made it's a different story, there's too much weight. I just use a wooden dowel rod to prop it up for the time being.
My solution comes with upgrading my bed to a more comfortable pillow top queen we have and ditch the thick 'matress like' thing that's there now. The new mattress weight is alot heavier.
I'm going to get 3 new matching gas springs in when I do the bed upgrade. I also need 2 spec'd for my dinette underseat storage lids. I'm going to add a couple nylon pulls with button snaps to the bed to make sure that it stays down during travel just to be safe.
I've found this place has a ton of misc specialty hardware for my shop projects. It's easy to search their inventory for the spring with the specs to fit your need.
3 of these will suit my new heavier bed.
I hope this helps out to getting you fixed up.
ps... as I reread your post, remember these are 'fixed force' springs and aren't designed to do the all lifting of their spec'd support weight(they do help out), they just hold the weight upon extension once it's gotten lift assistance when you pull to open your storage.