boost spikes

[sbiggi]

I have a question.... as you may or may not know my brothers 93 talon is an automatic, on high boost it spikes in between shifts.
When we have the boost set to hold 16 psi it spikes at 20 psi between shifts, why does it do this??? We dont let off the gas when it shifts or anything, is it just the rpm change after shifts??

thanks

by the way it has blitz dual sbc boost controller, 14b turbo, 450 cc injectors, and a ecu from a manual trans Eclipse GSX