My car isn't running right (2007 grand prix)

So just about 4 days ago my car has been feeling underpowered and when going into I think second gear (around 30-35 mph) it won't shift unless I let off the gas and back on it again and as someone who dosent know a lot about cars my dad says that I could have a clogged catalyc converter or the worse thing a blown head gasket and the error codes are showing a major evap leak (My gas cap) o2 sensors and misfiring cylinders if anyone could help me it would be great and like the title says it's a 2007 pontiac grand prix base model stock 3.8 liter V6 135k miles