Hello. I have a 79 f250 Crew with 3.54s. I just put new 35 inch tires on it. I plan on mainly towing around 10-12k pounds with it. It has a np205 and np435. Instead of getting axles with 4:10 or 4;56s, could I twin stick it and use low range for towing, and high range when cruising around town and on freeway to keep rpms low? I have no idea what my top speed would be with the rear axle in low and in 4th gear towing? Feedback please

Thanks. If that’s the Rpms that won’t work.