I don't understand what you're getting at or what you're even referring to in this post.. Let me rephrase my previous statements then; The transmission is working as intended.

 

First off whats slipping? I dont understand. And why not change ur exhaust back to your old one or why not get a bigger wastegate? What kinda ECU are you running? How is the boost set so precisely at 8.5 psi?

And lastly ur pushing it, your trans will not hold all that power. When it comes to Toyota's automatic transmissions, power is one thing not towards the top of their list of priorities. Neither is their manual but they still hold a decent amount of power.

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Yes torque converters intentionally slip at stop lights and initial acceleration. However on most modern cars once the RPM has reached a certain speed, the torque converter locks up and and becomes slip-less. This increases fuel economy and power efficiency.
He may not understand all the ins and outs of a torque converter but obviously, when he says it isnt slipping, he means that it is holding under boost and providing good acceleration.




you should not have to decrease the size of your exhaust to prevent boost spiking. Also at 8 to 10 psi there is no way a second wastegate should be necessary. Proper manifold design should provide for spike-less boost control. If a high boost application does indeed necessitate a second wastegate, this is something that should be considered in designing to manifold to begin with.
Decreasing exhaust pipe size or sloppily tacking on a second wastegate are both band-aid solutions to the true problem: a manifold with poor flow and design.