Um...either the gun is heating up and the frame is bending (NOT that uncommon with a TI gun, unusual but not impossible in steel!) or you don't have enough stamina in the muscles behind your finger tendons.
The latter is more likely.
There's an easy way to check: get somebody else to crank 20 rounds through it as fast as they can load and fire it, and then in your hands, see what it does.
If it turns out to be YOU, well, it's not really so bad. In that event, what I'd do is fire 20 rounds at my next range session and then just pause for bit, take a short break, walk around, watch other people shoot, in 10/15 minutes or so pick it up and try again. Don't get frustrated. Remember, your initial accuracy is fine and in a fight or on a hunt, *that's* what'll count!
If you're not practicing often enough at the range to affect your strength, fine, get some snap-caps and do 10 minutes a day of dry-fire drill. You'll get there.
What I suspect is going on is, you're getting tired, groups spread, you get frustrated, try and "overcorrect" and it all goes to heck. That's no good. You need a sort of "Zen calm" when shooting, in my opinion, both range and "for real". If you're not there, no sweat, take some time and adjust your mindset.