Congratulations on the birth of your sons and I am so sorry to hear of the loss of your son, Kyle. My thoughts are with you.
My thoughts on Jack's feeding issues (and of course, check with doc first):
1. Rouse the child for feedings. Preemies often don't feed "on demand" as they often sleep through feedings, so a schedule might be needed. There are techniques to gently rouse a sleeping preemie so they are in an appropriate state to feed. Make sure that you are using the appropriate nipple shape, flow and density (thickness) for your child's current needs so that he is able to get enough milk without tiring out, but also able to handle the flow without gagging. A call to the NICU OT, PT or Speech therapist who worked on feeding in the hospital could help. They might not be able to recommend a different nipple over the phone, but they could steer you in the right direction.
2. Talk to doc about baby's level of arousal, perhaps a low iron level or thryoid issue?
3. Infant massage has been associated with increased weight gain in preemies.
If you are not enrolled in Early Intervention, I highly recommend it. Request a PT or OT who is very experienced with preemies. You can also request to have a therapist come to your home to teach you Infant Massage. EI also offers Speech Language Pathologists for feeding as well as Nutrition consults with a registered dietician. If you have insurance, you can also go directly to a clinic who specializes in babies. I am not sure where you live, but I know Northwestern, UIC, U of C, Evanston Hospital and Children's Memorial have therapists trained in post-NICU care of babies.
Good luck and keep us posted!!