Well if the ignition switch is new, then that is probably not it. That issue would be due to a worn internal contact, which sounds unlikely in your car's case.
As for the heater blower being weak, there is one more very likely spot and it needs checking out. The power for the blower comes from its fuse a first runs through some electrical contacts built into the heat selection control where you select cool/heat/defrost (which is not separately shown on the mymopar diagrams). This is used to cut off power to the blower when the control is OFF. The contacts are integrated with the vacuum selector, and the contacts in this switch get corroded and hot and will melt the pastic body of that control. So you need to get the heat control out and look at this. This particular problem is very common. There are 2 wiring connections to the back of this switch and you can temporarily jumper them together and see if the blower speeds up.