2016 Cascadia Emissions Issues

I am having trouble with a truck. Last year it derated and a Truck Stop did a forced regen in NV. To be honest I'm not sure what started that whole chain of events but it sounded reasonable given the circumstances. During the forced regen the DEF lines melted at the fittings and started leaking def fluid all over. The shop then said they couldn't help and it needed to be towed. I then went out and was able to get the lines secure enough to move the truck and drove it a few hours home. I then replaced the lines (ouch they were expensive) and cleaned the doser and passage as best I could. I also replaced the DEF filter. I then cleaned then baked the DPF filters because I didn't know when the last time the filters were cleaned or replaced. The filters were reman units so had to be replaced at some time prior to my ownership. Some things I did more as preventative for the future since I had some down time. Everything was great until a few days ago, almost a year later and now similar problem. Driver get a 55 mph derate and tries to do a forced regen. Truck won't complete. Tries to drive to shop and gets a 5 mph derate. Shop comes out and says lines are melted. They replace them. Regen stops after 20 minutes and they're thinking it's the doser. Going to do that today and they say after the regen should be ok or know if there are any other problems. Any chance we are missing something? Truck is 10.5 hrs away so trying to get this done remotely but killing the pocket book. I do mostly my own maintenance so not afraid to tackle pretty much anything.

Any suggestions for other things we should do to the engine. Recently replaced the manifold and o-rings as preventative. Truck has just over 850,000 miles and runs strong but emissions is becoming near unbearable. Should I modify the emissions system and anyone know someone that does it right that can pm me? If you don't have personal experience, please don't reply on any mods. Not looking to seize the engine or crack a liner a week after a mod. Not planning to turn it up or anything, just need the reliability. Truck is in southeast AZ.