First try it without pulling down on the two take down tabs on the front half of the frame. You have to pull them down to disassemble the slide from the frame, but you do not need to depress them for reassembly.
This is the only thing I can think of which might be causing the hang up. Pulling down on them in the same way you do for disassemble may be what's causing the slide to hang up those last couple of millimeters. Provided everything else is in the proper place, barrel, guide rod, etc.
The slide should be able to simply slide all the way back as in full recoil and then come to rest in full battery as you release rearward tension on the slide.