Weather 2 tons is enough or not, can't tell from here for sure, but it sounds a little small from your description.
Depending what model Tempstar, it has a very good warranty. And the upper line tempstars are high quality units.
I would find out whats wrong, and proceed from there. The leak may never have been fixed right. Maybe they have a leak at one of their braze joints. If so, most companies will fix it at their cost.
Find out whats wrong this time. then come back and ask questions.