It’s very hard to pinpoint the problem online. Easier to eliminate possibilities. The STiOS has a lower center of gravity than the i20, and it also has a much higher playability factor, so I doubt it’s the club. Also, the XP95 shaft is light and provides a high launch, so I doubt that could be your problem. If you came to me, I’d check these things:
1) I’d make sure the epoxy bond was solid and there was no twisting of the shaft in the head. Unlikely, but has to be eliminated.
2) I’d compare the clubs’ loft, lie angle, length, swingweight and overall weight.
3) I’d check the ball strike you’re getting with each club using an impact label. I’d have you hit 4-5 shots off a short tee with the Ping, then the same with the STiOS and compare strikes and results.
4) As a teaching pro, I’d also look to see if you swing differently with the 2 clubs. This is not uncommon.
5) Unless you experienced the difference on the range where the balls are the same, I’d check the balls you used in each instance you referred to in the post. The ball can make a huge difference!
6) Finally, I’d also hit your new clubs and compare them to a similar club I’ve built from my demo set.
If you have a teaching pro you go to, you might consider asking his help in a similar way to the above.
Hope these ideas help. Michael