I'm in agreement with the others. I would think the EcoDiesel would be a good match for your application. The following is a Torque/HP comparison of the 5.7 Hemi, GM 5.3, and the EcoDiesel. The spec's for Eco are from 2020, so your 2018 will be down a bit on power (20 - 30 hp).
The little Diesel makes power at lower RPM's. It likes the 3000 - 3500 rpm range for hauling grades. The gassers are typically spinning 4 - 5K under similar conditions.
The advantage of the turbo diesel is that it won't be giving up 3% of its power every 3k feet of altitude.
The elevation along I-90 in Washington isn't all that extreme (3000 feet?). You said East bound, so the wind was likely at your back. I'm thinking you are having other issues. You mentioned the truck was lifted. That's not normally a great move for a tow vehicle, but you have an 8 speed trans to make up for tire size increases. Any chance the speedometer wasn't corrected? Beyond that, it would be interesting to understand your speed/RPM's in gears. It's possible the transmission wasn't downshifting properly.