You won't see 28psi with your stock turbo and your set up, if you do it won't be for long!! Nothing above 25 is recommended for the stock turbo, and most tunes won't spin the factory turbo that fast. 1250 is sustained redline for the EGT's, short bursts to 1400 is okay but nothing sustained. Average trans temps are 70-90 above ambient, 70 for unloaded and 90 for loaded down, although anything below 200 is fine, sustained temps above 200 and I want more cooling.
You didn't say what tunes you were running with these numbers, if it was a aggressive race tune they may be inline, your larger tires will raise boost a bit because it is working a little harder to turn them. My boost will run under 5lbs cruising down the highway. If you can get EGT's to 1250 that easy I think you need more airflow. All the sharp bends with stacks can cause some backpressure, where does your system go to 7"? If it is just the uprights and the rest is 4" this may be your problem, or it could be tuning. Proper EGT control is a mix of good airflow and proper tuning. With my set up I have never seen 1250 or had to back out of the go pedal. A that is towing heavy up some steep mountains. If you need more info PM me.
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