Recently I have had my Evo 8 with UTEC professionally tuned at TurboXS. The latest issue that I have had is that when downshifting from say 5th to 4th and getting on it the boost spikes very high ~ 24psi and there is what sounds to be a backfire followed by a sudden decrease in acceleration.

Can anyone provide me with some ideas of what is happening? Is this boost cut?

Mods are as follows:
3"TBE w/high flow CAT
Helix lower and upper piping
MR BOV
K/N Filter panel
255 walbro
650cc FIC injectors
264+ comp cams

Put down ~ 300hp and ~300 tq. on a dynapack at 22psi