Hey ww77, i have experienced this exact same thing. My car also has an Uprev tune. Actually, i've had this happen on two separate occasions.
First time:
I got check engine lights and other lights came on in the dash. Happened multiple times. Turning car off and on did not help. Had a throttle position sensor code. The fix that time was to replace the throttle body (throttle position sensor).
Second time:
Just as you, no check engine lights or any out of normal guage readings, it just loses power out of nowhere. After turning car off and then back on, the symptoms are gone. After discussing this with my tuner, they informed me that there is a "fix" that can be installed with the Uprev tune. It basically has something to do with the MAF's relaying invalid readings to the ecu and the ecu killing power.
Check with your tuner to get the fix. If anything, get a hold of Uprev, they should have the details on this fix.
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