Be sure the vss is setup correctly, meaning, the rear vss is the original vss, meaning it should be on the tailshaft.
The two wires you mentioned are for the front vss, the ISS, this is the speed sensor near the middle of the case, those two wires go there and to the pcm.
The original vss, the rear one, the output vss, goes to the pcm as well, but you shouldn't have mess/moved with that one, it stays in it's original connector pins.

What gear does the trans start off in when you put the truck in Drive, if it's slow, probably second gear.

let me know,
allen