I pull a 5th wheel with a stock 97' with a 3. 50 rear axle and am thinking about having it swapped out for a 3. 70 or a 4. 10 to increase pulling ability especially on hills, etc. Would I really notice much increase going to 3. 7? What would it cost in most areas to have it done. I am concerned about going to a 4. 10 due to higher rpms at normal cruising speeds, lower gas mileage etc.