My truck overheats when hooked to my travel trailer,not my 22 foot boat or my trailers.sometimes it will only go 12miles,then it will go 60miles or so.ive changed out the clutch fan thermostat,res tank and cap,water pump check out fine.not sure if it's the radiator or head issue or injector cup leaking.the only leak is from the pressure at the cap and only when pulling the travel trailer

Had this problem with a Chevy suburban when towing. Found out the radiator was clogged, and had to replace the radiator. After that there was no problem towing.