The S4 now has a mind of its own... At 3.5k to 4k rpm, the engine is gasping for air, and hesitates. Button-Shifting during acceleration is useless. The car shifts when it is good and ready. In 5th, the slightest attempt to accelerate, gently, say from 70 to 75 results in a downshift and a neck-snapping lurch forward up someone's tailpipe. Normal? or needs work?

 

Wow... now there's something I don't see everyday... something bad about the GIAC tip chip. Was this how it was when you first got the chip? BTW, what year is your S4? The lurching and stuff sounds almost like what my S/C'd Solara did when the O2 Sensor failed on my car.

 

Welcome to the forum ssss !

Like Cirek said, we need a bit more info on the car... Year, age of chip(s), other mods, recent maintenance....