In July i went up the Green River Gorge on I-26 in North Carolina it's a 7% Grade. Coming from South Carolina. I was doing 3000 RPM at 40 MPH in the right side truck lane. My truck is a 2002 Dodge Ram...
You have around 210-220 HP at the crank at 3000RPM Maybe 170HP at the ground 14,000 lb requires 105HP to go up a 7% grade at 40MPH This leaves you 65 HP which is about enough to cover drag at that speed with a truck/camper combination.