I have an '11 GT 5.0 purchased in November of 2010. The engine revs seem
to decrease very slowly when you take your foot out of it. Does anyone else
find this to be true with their 5.0? Does this have something to do with the
throtle by wire? Last mustang was a 2001 Cobra.
It's been that way since Ford went to drive by wire but is easily fixed in a tune. I think they tuned it that way so grandmas could shift smoother. Same thing for having to press the gas pedal b4 anything happens:less chance of stalling the car on takeoff with a stick. Again, a good tune will fix this.
I find my '11 seems to accelerate with little to no throttle lag. Same for rev-matching downshifts. It seems to be pretty accurate and lag-free. My '07 had a noticeable lag under acceleration (at times)...and for sure on rev-matching downshifts.
A lot of the throttle lag is do to the fly-by-wire that was introduced to the mustang back in 05'. Each year it has gotten a little better from the factory, but the only real cure is a custom tune. A strategy tune will improve it, but with a custom tune you are able to adjust the throttle response specifically. I've driven cars that had the throttle response so tight, when touch the throttle it peels the tires, and everywhere in between. Most tuners will just have a setting they use for everyone, so if you want it to be tighter, or in some cases not so responsive, you'll have to request it (same with shift points and pressures on autos).