You may also want to look at what your final drive gears are like. I have the same setup as you and swapped in 3.73 gears before my 351 would pull weight on the highway. You may want a higher gear ratio if you have larger tires on your 250. From stock to a crane 444232 with 3.73 gears made my truck feel like a new torque monster. I aimed for 3000 rpm at 65 mph.