The 4.4i is essentially bullet proof. I have over 62,000 miles on my 2001 4.4i with Dinan throttle body, engine and transmission software (aprox 300 hp and 350+ lb ft of torque), and have pulled a 31 foot 8,300 pound GVWR travel trailer for over 22,000 of those miles getting an average of 10 mpg at an average speed of 64 mph when pulling. Without the trailer I get 18 to 22 mpg highway (wind dependent) and 14 to 17 mpg city (stop light dependent). It's still rock solid and only consumes about 1 pint of Mobil 1 15W-50 engine oil between 6,500 mile oil changes.

Only problems have been the cooling fan recall (twice), a right cam sensor failing, the coolant sensor failing and the coolant reservoir sensor float failing, all of which were nominal items covered under warranty except for the last item which cost me about $75 but was easy to replace (all quick couplings).

I recently drove the 2005 4.4i non sport and didn't notice any appreciable power increase. I max throttled it but didn't "wring it out" rpm wise which may have resulted in more dicernable power. Due to my 2001 torque being equivalent to the 2005 the initial "take off" felt the same, save for a hesitation in throttle response of the 2005 from a dead stop (my Dinan throttle body increases response).

As a result, the 2005 4.4i gave me no reason to consider trading up to it.