I am having same problem out of my 2012 GU713, MP8 505 Maxidyne, runs good till comes up to temp then first hill falls on its face, changed turbo at a sum of 4300.00 for pos turbo, tech told me turbo for sure well not turbo money wasted. I pulled the egr cooler flushed at car wash truck got back about 75% power on hill always did good on flat loaded or empty hot or cold....
so going to replace egr cooler but dealer quoted 1600.00 plus tax and shipment charges... thanks a million WorldWide equipment what a joke for dealer!! Found online for 1000.00 total with shipping.
So long rant short check egr cooler and egr valve..
OH by the way downtime is a way of life if u buy new Mack equipment I have owned Mack my entire life as well as my father.... I would have never said this of my RD800’s but the new Mack equipment is Junk pure Junk.... they are rags, will not hold together in the coal or oil fields Mack Trucks and WorlWide equipment Inc. sold us equipment for a job they knew these trucks weren’t designed to do. THANK YOU Mack Trucks for lying to us!