Duramax low rail

Just flashed a tune into a lbz duramax commanding 120 mm3 and upped the duration near 20% more. Upped the timing 5 degrees and the desired boost. On test drive under full throttle it’s commanding 26,107 psi and made it to 25,000 psi early in the pull and then fell to 10,000 psi very quickly but made it back to 23,000psi by the end of the pull. Is this a relief valve opening?