Sounds to me like you may be underexposing - check your shadow detail - is it weak or thin?

I shoot a lot of 35mm and 120 rollfilm Efke 100 and Efke 25. I don't have any problems with neg curling. I use the Ilford fill, soak and dump method of washing after fixing. I do a final rinse in distilled or deionized water with 2 or 3 drops of low foam wetting agent added (I use Edwal LFN). I hang my negs to dry with weight attached in a dust free environment. When the negs are dry I store them flat in a NegaFile.

I use a water rinse instead of an acid stop bath (because I normally use Pyrocat which is a staining and tanning developer).

However, there's nothing wrong with using a stop bath with the Efke films developed in D-76 or other non-staining developers. In fact, an acid stop bath may be required for development control (to stop the development) if your development times are short.