Transmission Line pressure during shift 4L70E

I have a question related to line pressure.

I have a 400 psi gauge on my freshly built 4L70E in my 2008 AWD TBSS. A friend had nearly the same freshly built transmission in his 2007 AWD TBSS. He had the trans shop tune his and I am tuning mine.

The issue. His tuner saw a dramatic (~30 psi drop during shifts). He was concerned and "fixed" it. He was using EFI live and did not have a solid explanation on the fix. I have the same pressure drop.

My question is, is it normal to see a pressure drop during a shift on a stock trans? How about a shift kitted/built trans? What causes the pressure drop? Is it bad/good/indifferent? I am seeing around 180-200 before the shift, a quick drop into the 150s and then right back up. I have tried disabling adaptive pressure, changed shift times, adjusted modifier tables, etc.

Any help is appreciated! :cheers:

Look at the Cool Aid post this might give you some information.

Thanks,
Mr. 2008 SS

I have seen CoolAid's post but he doesn't delve into pressure tuning, especially with a gauge. I have done an exhaustive search and found nothing on this specific topic. It's quite peculiar though. I thinks it's normal, but want to be sure.