Here are a few tips to raising your Pokemon levels fairly quickly, though it's still slower at higher levels, but faster than before. Take the Pokemon you want to train and put it at the front of your party equipped with EXPERIENCE SHARE. Go to the Elite Four (Pokemon League) and battle them. The Pokemon you are training will come out first switch it with a stronger Pokemon in your party. Then continue to battle. This way the Pokemon you're training get exp. for EXPERIENCE SHARE and battling a little bit. Also trade Pokemon you want to train a lot the more they are traded the more experience they can earn. My level 91 Riachu has been traded about 5 times and can level up 3 time at the league by itself. Hope it helps!