You have no clue what you are talking about, he is correct. That oil is too thick for the cam phasers, it will harm the engine. Many diesel oils have higher ZDDP content, this will harm catalytic converters.
The 150/1500 has IFS, the Ford SD/Ram HD use a solid front axle. If you spec an HD gasser right, it will cost no more than a 1500/150.
My next truck will be a Ram 2500 6.4 hemi, the 8HP75 (ZF 8 speed) auto is rock solid.
Cheapest and -40 do not play well together. I plan on keeping this truck a long time, cheapest won't be getting bought. I'd rather pay more for a full synthetic for superior cold starts.
Next change will be Rotella gas truck 5w30, the change after that will be Amsoil.