Digital dash blinks on and off everytime i use brake pedal

You probably pinched a wire when you put the bed back on. You most likely have a blown fuse as further proof that you shorted out everything in the back of the truck.
Recheck all your wiring paths.

do you hear a clickung sound everytime you step on the brake pedal?? get into the truck and be very quiet. turn on the key so the dash lights up and turn off all accessories such as radio and heat so its totally quiet in the truck hit the brake pedal and listen for clicking sound coming from shifter area. if no sound is heard at all than your solenoid to release the shifter from park is not working. start with doing the test and post results.

Sounds like you have a short somewhere in the brake circuit. May be between the brakes and the blinkers in the brake lights.

first check the bulbs, turn on the hazards and lights,see what doenst look right. maybe bad ground, check the ground connections at the tail lights.

Check the pedal assembly bolts they may be loose or a weld has broken under dash . Check under hood have some one depress pedals watch for movement that may not be normal .

check the bulbs or the sockets for damage
or the wrong bulb
you are getting feedback through the wiring
and that lights up the dash

hi poss one or both brake light bulbs filaments are touching causing a back feed note if the brake lights are on the cruise control is cancelled

Check under the drivers pedals for a plastic switch around the brake pedal. This operates the brake lights. It may be out of adjustment or broken. There should be a gearshift lockout to require you to step on the brake pedal to shift out of park. There should be a switch either under the hood or dash for the shift. Check with an autoparts place and they can show you the two switches so you know what you are looking for.

make sure emergency brake pedal is pulled all the way up