radiator smell when pulling load 04

[Tyjack]

Truck is a 04 6.0l with 88k. I can pull a 4000lb boat no problem, when i hook onto my 10,000lb camper it never overheats or looses any fluid but in the cab i smell radiator fluid. The dealer cleaned EGR, still happening, so they replaced EGR, HEAD GASKETS, AND BURB JUG. Still smell this radiator smell. In the begining the dealer witnessed smell with my camper behind truck, now dealer is saying he cant replicate smell with or without load. Any advice would be grately appreciated

[2005F250]

Heater core or maybe the radiator cap is bad.