I think Gene had mostly overcome his fear of jumping because he felt pressure to keep up with Finny. Until the end of Chapter 4, Gene had the impression that there was a friendly but competitive rivalry between himself and Finny. Gene is jealous of Finny’s effortless athletic talent. Gene is also jealous of Finny’s self-confidence, how he gets away with things and Gene is mostly jealous of Finny’s innocence. Gene has, in his own mind, manifested a personal war between himself and Finny, mainly because Gene assumed (incorrectly) that Finny was trying to sabotage Gene, thereby topping Gene in their so-called rivalry. Any time Gene overcame a fear in competition with Finny, it was an effort to get the best of Finny. Of course, Finny had no jealousy and never took such competition seriously.