Loss of Power Issue - Oil Temp

[muttinthehut]

First time poster and need some guidance. I have a 2015 EcoDiesel with 150k that I purchased used. I use it to tow a small travel trailer with a UVW of just under 5k. Truck runs fine around town without towing, although the oil temp seems a bit high. On my most recent trip, I experienced considerable loss of power at times down to 45 mph, especially going up hills. The oil temp is way too high (270 range) and I've read that this excessive oil temp can cause this issue due to derate.

I have read a few posts regarding this issue, but can't seem to identify a true "fix" for this issue. Will an external cooler help (if one's available)? I've heard the GDE tune might resolve? Any thoughts or suggestions?

Thanks,
Mutt