Cm 2350 derate with spn 1209

[farmtrucknw]

Have a 2017 Prostar with the 415st isx 15 with about 357k miles on it. Had a couple instances where it throws the 1209 code with a derate so I changed out the exhaust back pressure sensor and the egr delta P sensor while I was at it. First trip truck felt a little stronger and thought that must have solved it but threw the same code with derate again. Just like prior times I pulled over, shut truck off and back on on, code goes away and off I go again. What do I need to look at now? My slip joint is leaking from manifold to egr cooler which i need to address but could this be part of problem too? Before I changed sensor out I had a neighbor do a forced regen with incite and it passed fine. Truck does have emissions intact tuning up to 475 hp and has for about a year with no issues. Any help where to look next appreciated.