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QB78 Deluxe Power Issues

Hello all,
First real post - new to the forum.
Have a nice .22 cal QB I purchased several years ago from very reputable source up in NY.
Came with upgrades (XP tuned Valve, Bolt). 
Had a leak awhile back after thousands of rounds. Ordered and replaced valve, applied reseal (purchased kit) on rifle - no leaks!

**ISSUE: Rifle burps out first string of pellets at a blazing 30FPS (yes 30), and requires around 20-30 shots to "come up to power" before stabilizing at an acceptable level where it groups awesome as it should. I do not have a chrono, 30FPS is a guestimate.

Basically, when I load C02 cartridges I need to dry fir the rifle 20-30 times before pressure stabilizes. I do not hear any leaks.

Anyone have this issue? Would love to self-help before sending in for repair, but not opposed to doing that either.

I have several other rifles to keep me busy, but incredibly, this one has been the "gem" of the stable among powder burners and PCP's. 

Thanks in advance for your valued input!
Best regards,
Scott