96 GT Bogging problem, help is appreciated

[eloggia]

I would appreciate some help anyone could give me on a problem I am having with my Mustang. I have a 1996 GT with the PI engine upgrade package, just in case that is relevant. I am encountering a bogging of the engine usually when I am on the highway in high gear and I let my foot off the gas. The car acts like it wants to stall, but won't. I also get the same effect when I am in a low gear at high rpm and let off the gas, such as driving through a parking lot. The car runs strong and sounds fine other than this problem. I have been told that perhaps it could be the clutch spring? I don't have a clue, but I have spent many hundreds of dollars working out all the ticks from the install of the PI package and I am getting frustrated. I would thank anyone willing to take the time to help me out if they are able. Thank You all Eric Loggia