The simple facts are that heavily loaded modern gliders need a ****load more speed than older light wingloading gliders.
Some tug pilots seem to not know the difference.
When I am in the tug I reckon I can feel when the glider needs speed but after many tows from the glider end I can see that not all tug pilots can see this.
Brief your tuggie or potentially die! I have lost one friend and seen some crappy launches at comps.
The JS1C at max weight needs a pawnee to fly at 75kts for the glider to feel good, my ASG29 needs at least 70kts, club tuggies might be more used to
Blaniks or the like that will climb OK at 55-60. Use the flaps as instructed by the flight manual.