Dodge: Truck not heating up enough, radiator cap, vacuum leak

Question
1994 Dodge Dakota 318 eng.
Why won't my truck heat up? Put 2 new thermostats and had radiator cleaned. Also replaced radiator cap. Only repair lately was new transmission. They ran fluid through new trans. cooler instead of radiator. Should that make any difference? Had new evap. for ac replaced last summer and they put in new heater core while the dash was torn apart. Heat comes out but not as hot as it used to be.

Answer
I was thinking the heater core but read you had it replaced.Usually it is one of the symptoms you mentioned but it now will have to be in the temp selector on the dash,or either you have a vacuum leak under the hood and the flapper is not functioning properly.