First, I don’t know the characteristics of the Alta shaft, so I can’t compare the shaft specs to the Recoil 65. Obviously they are the same weight. Loft is the major factor in iron distance. Shaft changes, unless changing from one weight to another (like 30 grams difference), or flex difference (X flex to A flex if the A flex is the proper fit) will rarely result in more distance. Even in the two scenarios I just mentioned distance changes are not nearly as much as they should be when considering the lofts. We know that a 1 degree loft change generally changes distance by 2.5 yards. Of course, there are always exceptions. Interesting that you still hit the TE’s as far as there is quite a bit of difference in the lofts between the two models. I have to assume the length of the clubs are the same, as length can affect distance as well. 1/2″ club length difference can affect distance by approx. 1.5 yards.
So, I do not think changing the shafts in the Ping irons will yield any significant distance increase, if any at all. If the Alta shafts were 95 grams and your were going to a 65 gram shaft, you would see some difference, but not since they are the same weight as the Recoil. I really can’t explain why you wouldn’t hit the Ping further with the Alta shaft simply because of the loft difference between the Ping 425 and the TE. I do know the the TE irons are a great club and still one of our best sellers in this age of strong lofted irons. It is stable, forgiving, solid. Might just be that you swing it better and hit it more solid more often. If you want to try something else, our new KE4 MAX iron is long, and very solid. Similar lofts to the PING. Since you don’t hit the Ping farther than the TE, no guarantee you would hit the KE4 MAX farther, but my experience in testing with the MAX is that it is longer, for me, compared to my DBM irons, which are basically the same as the TE with 1 degree stronger loft.
Apologies for not having a clear solution, but hopefully this helps.