It's a VEEEERRRRYY quick shift.. Not a full throttle powershift but damn close. That and you have to be spooled way the hell up in second, near the rev-limiter, when you nail the shift or the gearing in 3rd will get you. Mustangs are notorious for their 1st and 2nd gear acceleration but they tend to dog (relatively mind you) in 3-4-5.
At least that's been my experience through my friends 84, 86, and 95.