The best upgrade to get HP is an engine swap...
Also, when chips claim a 28hp gain, its not a PEAK gain. Like if your car has 125hp a chip doesn't make it 153hp. The gains are in the mid range, and the peak gains are small. Like on an M20B25, chips claim a 15hp increase. Well, that is at like 4,400 RPM. You actually only gain 2-3hp at the peak, making it go from 168 to 170-171 theoretically.