I have a 2005 sport, 4.0 with a K&N filter on it. When I am at highway speeds I find I have to punch all the way down on the throttle to get to get moving and it feels like it is struggling hard to get going even if there is little to no wind on small inclines. I have tent trailer (1000 lbs) that I have pulled before with it and it struggles hard going up hill. Is there something I am missing? Thoughts?