Heater throwing out cold air put in a new thermostate work for two days throws out cold air again what might be wrong? Also when heated up the truck dies. At a stop light it also chugs like its going to die. Also when I step on the gas it should be at a steady speed and it kicks down or outin speed like the gas pedal is sticking.
Have you checked the coolant level in radiator? If bleeding of system was not performed correctly or you have coolant losses issues, the problem would occur.
Check for control cables broken or out of adjustment, heater hoses leaking or clogged and faulty water pump. Also check for broken air dampers, faulty servomotor (some models), clogged air ducts, leaking or clogged heater core and faulty heater control unit.