94 z24 heat problem

i put a new heater core in my car because it was leaking, well after i did that i have heat but its not hot like it used to be...i put a new thermostat, and still nothing, it feels like the blend door isnt opening all the way, is the a way that the cable could of streatch..any tips. thanks

Is it possible this style heater core has a flap that only allows it to flow one way? If so, the hoses could be reversed..... Don't laugh... Ford does this on the 92-up Crown Vics.....