There are thermostats on the market that are rated higher than the stock replacements, I'm not sure where to get them, but I'm sure they're not at the dealer. A couple numbers are popping up in my head, stock is around 160ish degrees, and the higher aftermarket is 190ish maybe?? I can't remember exactly.
Something else to do, is clean out your heater core by removing the 2 hoses at the fire wall, and spraying water through one of the pipes, and water and junk squirts out the other. A member here did this to his sister's tracker, and it made a difference.
You could also clean out the blower box, and blower motor, use compressed air on the blower motor to get off any thick dust, that may be slowing it down.