I would say go for a dual rear axle, updated brakes all around, and a goose neck trailer. Something that will put the traction down to the ground and the load weight over the drive wheels should help you up that hill without needing in to have a 4x4. Should give you better stability and control at highway speeds, not to mention a better than 10K max towing weight. But seeing as you already have a trailer might not be the option you're looking for.

just my two bits smile

1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P