Velocity variations

When I first got my .22 Talon SS, it shot Superdomes at around 830 fps, Kodiaks around 740 fps, and Predators at around 800 fps after I lubricated it and adjusted the top hat. This seemed a little slow compared to some numbers I had seen, but it was shooting very accurately, so I didn’t mind. A couple of months ago, I put on a new scope, and in the process of dialing it in, I chronied it again. This time, all of the speeds dropped around 25 fps. This seemed odd to me, but the gun was still shooting to the same POI and was grouping well, so I didn’t much care. Well, just the other day, I took it out and chronied it, and the velocity had dropped about another 20 fps. Not only that, but every 20 to 40 shots I would get a low powered shot, ranging from 500 fps to 150 fps! So, I tried a different lubricant, to see if that had something to do with it. Didn’t help at all. I tried adjusting the top hat, in case it had turned in the process of being shot. But it turned out that when I found the optimal setting, it was the one I started with. So today I tore the whole thing down, cleaned off all the parts with rubbing alcohol, cleaned the old lubricant out of the body, polished the barrel where the breech sits, re-lubed everything with dry silicone lubricant, and put it back together. Now, Superdomes are shooting at 790 fps, and the Predators are shooting at 765 fps, which is STILL 35 fps slower than what I started with, and 10 fps slower than what I had a couple of months ago. Adjusting the preload doesn’t do anything, either. So, my question to you, the Airforce Braintrust, is this – What can I do to get my velocity back? I don’t need blazing speed – I would just get a Condor if I wanted that. But I do want consistency, and I would like it up around the velocity I started at. Does anyone have any idea what is going on, or anything they think I can do to remedy my velocity woes?
Thanks in advance,
Chris