Everyone thinks a 300 hp motor will make anything really move. Thats not always the case. It depends a lot of stuff - the gear ratios, transmission type, vehicle weight (power to weight ratio), hp/torque curve, etc. I really think the big problem with these SD is that the 5-speed auto keeps gearing too high too quick (set more for fuel economy rather than performance) - they dont want to down-shift unless you stomp on the gas. For this reason, try the tow/haul mode to see if it is better.

These 5.4L SD has a towing capacity around 10,000 lbs + around 6,000 lbs vehicle weight = 16,000 lbs for a 300 hp motor...not a good power to weight ratio at all. The motor can handle it but it will be slooooooooow.