Roadsport

I just started using my GT (Saleen S281), which is my only non-classic Mustang. It feels like the rpms stick unchanged for a few seconds, when I take my foot off the pedal. It makes for stupid sounding gear shifts, when rpms don't drop off. Is this a normal behavior for these models? What is the likely source of the problem? (cable sticking, flow meter trouble, ignition...???)
Thanks in advance for any help/pointers.
/Ken