Why not just make it 60 range like other TDs? Simple and finally giving a 60 range tank destroyer to ost. If you really insist it could be temporary (sth between su85 and US at gun).
I honestly think this is a bad solution. Please correct me if I'm wrong (I don't have the exact numbers at hand right now), but the StuG always or at least very reliably penetrates Allied armor except for the very heavies, which is its intended role. Increasing the range to 60 would make it very similar to the JP4 and only be possible with increasing the fuel price accordingly.
In my eyes, the reason why we don't see much of the JP4 is that it has no real role on the battlefield. It is quite fiddly due to being a casematte, too expensive to buy for just countering mediums and has too less pen to fight against heavies. The Panther is more often a better choice because while being more expensive, it's an overall less micro intensive and allround better unit. The only thing that a JP4 can do better is countering Allied TDs, but that's it.
StuG would suffer the same fate. Right now it has a very good niche. A Casematte to counter mediums. A bit fiddly but being cheaper than the unit it counters. And it also performs well in that role. If TWP really is a big issue, than it should be buffed or exchanged for another ability. But keep in mind that the overall performance of the StuG should remain the same (assuming here that the StuG is decently prices for its performance)