YMMV, but many men -- myself included -- have had success curing or at least improving this. For some it takes longer though, and even once the physical issues are gone psychological issues may remain. Some ideas that you may have already tried:
- Stopping porn and death grip masturbation (sounds like you're already here)
- Practicing mindfulness meditation to help you get out of your head and relax. This may have other life benefits as well so it's worth considering.
- There are some penile lotions/moisturizers that can improve skin health and increase sensitivity.
- Talking/communicating with your partner better so you don't worry about what she's thinking so much
- Practicing good oral beforehand so you feel comfortable that she's reasonably satisfied, and from ^ won't be too upset if you don't perform. This really helped ease performance anxiety for me, which in turn led to better performance.
- Exercise regularly so you don't feel out of breath and too sweaty if it takes 30+ minutes of activity to ejaculate.
Most of these have side life/relationship benefits so they're all "might help, unlikely to hurt, worth working on regardless".