Need help with braking system

Alright, so I'm having an issue here. A few weeks ago, I took my truck in to the stealership because it was really hard to brake (to put it into perspective, my friend's old car without power brakes was about as easy to stop). They looked at the braking system and said that the rotors were fine (no thumping while braking), the drums were fine, and they bled the brake lines. The pads were almost new. What they did notice was that the caliper pistons on the front disks were seized up, which should have been the reason, so I went ahead and gave them the OK to replace the calipers. However, after I got the truck back, its still just as difficult to brake with. Does anyone know what could be the matter?

 

Brake booster maybe?
Seen some posts about it.
My father in laws taco just got one last summer.
Mine is still stock.