I have a 2005 mustang gt 5 speed that is stock. I would say it seems that it does this when it is not warmed up yet to normal operating temp...but if i would be in 2nd, maybe 3rd and would get on it a little bit, around 2800-3000 rpm it does what seems like a slip up and drops a lil in rpm and then continues to rise up again all the way through the rpm range....I live where it is around a solid 35-40 currently at mid day so it is rather chilly....i didnt notice the car doing this once is was warmed up....any idea whats happening there???? Basicly I can drive along at 2000 rpm, and step on it, and it gets a scootin but hits a **** spot and drops rpms, then starts to pick up again...It does it rather quickly as I can still get up to speed fast but it doesnt seem that it is normal...

 

It could be since the weather is chilly and your tires would not be warmed up a whole lot, that you are getting a little wheel spin.