If you don't have any middle speeds on the fan control, then you need a new Resistor,  It's located just above the pass. floor boards, behind the fan itself.  To best get to it, do the head stand in the truck. 

But if you had the dash apart, maybe you didn't get the tubes back together, or some of the cables came loose.  Which is a pregnant dog. 


But, as with most of your posts, we need some better clarity on the situation.