Very happy 2011 390 RB-40 owner. The 340 Cumins is fine you'll slow down in the mountains but it is no problem. The 340 Cumins has 5,000 lbs tow limit due to the Allison 2500 transmission. The 360 Cumins has an Allison 3000 transmission and tow capacity is 10,000. I don't know if they changed since mine was built or they are still the same transmission.
2011 Berkshire 390-rb-40, upgraded tires and front axle airbags, 2012 Jeep Wrangler 2 door, Blue Ox baseplate and BlueOx aladdin tow bar, Blue Ox Patriot brake system, wiring run through right frame rail and homemade led taillight bar.FB.