I usually run tubeless around 30 psi.
Grips are a personal thing and what each person finds comfortable is not particularly relevant. I ran ODI Ruffians for years until I rode the Intense grips that came with my Primer. I quickly used my dealer contact to pull some strings and order a pile of them as I love them (they aren't the same ones on the Intense website). If I can go without gloves even better. Even riding DH (once in awhile my childhood BMX roots come out). But if conditions are really hot and the grips get sweaty I'll wear gloves.
Carbon bars should also help, but IMHO it depends on how often you crash. Unlike many normally long-lived parts on an XC bike, bars on a DH bike are somewhat considered wear items. A few good crashes on them and they should be replaced.
Honestly, the two biggest things with hand cramping is braking technique (not using them) and getting more relaxed and keeping a looser hold on the grips. Both come from experience.
It's possible the fork could use a rebuild. Depending on how much you're riding, a DH fork will usually need to be rebuilt once a year. Check the spring pressure as well. You should be using all of the travel at least once per run, if not more, although you shouldn't feel the fork bottom out harshly.