can someone tell me what i did wrong tried to rebuild my trans after breaking rear shaft in half so i swapped out the broke parts now the truck want back up at all if i want to back it up i have to pull the driveshaft so whats up

 

How does it do forward does it start in 1st or second Sounds like the band is applied , If it is the reverse inout drum will not be able to turn and you will not be able to move backwards. Possibly a misassembly of the 2-4 servo assembly . Take the snap ring out of the servo and remove the servo assembly now see if the truck will roll backwards.
Another possibility if the three longer bolts in the valve body with the 8mm heads are miss located it will cause the same symptom by jamming into the gear train. Do not attempt to drive untill the issue is solved