I had a 5.4 with the 6 speed and 3.55s. No real complaints at all- but it did run out of breath in the upper RPMs.
I had a totally different transmission, but I wouldn't be afraid of the old 5.4. It was a great tug engine and the 3.55s were adequate for our TT. Not a rock star, but not underpowered by any means.
I drive a goat now...