Lml overheating while towing

Hey guys I’ve searched and can’t find anything that is helping me so please help me out. I have a 2011 duramax lml and I am having. A overheating issue we can’t seem to figure out. When I am pulling my 5th wheel that weighs 15,000 pounds up grades my truck starts over heating the temp has got as high as 248!! I have cleaned the cooling stack, and replaced the fan clutch and still no luck. The truck has mods such as full delete, 5inch exhaust, ppe down pipe, ppe headers and up pipes, s&b cold air intake, banks intercooler, hsp intercooler piping and y bridge kit, fleece performance 63mm cheetah turbo, ezlynk with ppei tuning, fass 165 lift pump, lifted on 37inch tires and 456 gearing. I was told it may be my torque converter causing the engine to work to hard and making it over heat? I have spent a lot of money on this truck in the last year trying to build it into the ultimate towing rig and it’s not working out in my favor. Please help

Your fan clutch is ECM controlled and should be engaging.

Lift and big tires not a good tow rig. lots of cooling air flow issues.

Aftermarket turbos tend to result in high EGT and the LML in general does not like to have these things messed with.