Nothing wrong with the 5.4, imo. I have the 5.4 in my current f150 that has a small lift and the same 35's that come on the raptor. I have only added an edge tuner,roush exhaust and k&n cai and it runs good. with the tall tire and not having re-geared it to a 4:10 the edge was a must to get the power and shift points to compensate for the larger tire. I test drove an 09 that is suppose to make a little more power than my 06 version but my truck felt much better seat of the pants than the newer 5.4.
I am holding out for the 6.2 because it is going to be a truck I plan on keeping for a long time and I have been reading and waiting for this new engine from ford for quite a while. My opnion only (no offense to you future 5.4 owners) why have a performance truck with a non-performance engine? sure some guys my spend 6k to SC there 5.4s but 3k and 400 hp is worth the wait for me.
I asked the same question several months back, with no real answers. Two weeks ago i had my F450 in for service, so i rented an F150 with the 5.4 for a couple of days, after driving the F450 with the 6.4 diesel, the 5.4 motor felt slow and sluggish compared to the F450, even though the F450 is a much larger truck it feels more nimble and wants to get up and go. I personally feel that i would be taking a big step backwards as far as engine performance goes, it`s just hard to go back once you have felt the HP and TQ, i think that the 6.2 will equal or match the performance of the 6.4 diesel that i have gotten used to driving. Taking nothing away from the 5.4, it`s just my experience with my limited time driving with that motor, who knows the 5.4 could be a better off road motor, size and HP does not always make for a better motor off road.