Just completed installing LED rear lighting on a 2001 Dodge 3500 with a new flatbed.
The stop-turn-tail lights are double TruckLite Model 6050.

Flasher flashed at a fast rate, like it was designed, indicating a bulb had burned out because LED lights draw far less current than incandescent bulbs.

Went in search of a flasher compatible with LED lighting, nothing available locally for a 5 prong flasher.

A search on DTR indicated resistors in parallel with the LED lights are necessary to create enough current draw to make the flasher function properly.
Well, being cheap I wasn't going to give RadioShack $20.00 for a couple of resistors.

The solution: Salvaged one of the old rear turn signal/taillight bulb sockets , wired each side of the dual element bulb (3157) in parallel across the respective turn signal circuit.

Was concerned that there may not be enough current draw across the tail light element portion of the bulb since it only draws .59 amp as opposed to 2.1 amp for the turn signal element to make the flasher function.
One side now draws 1.37 amp(2 LEDs @ .38amp each + 3157 bulb taillight element @ .59amp), the other side drawing 2.86 amp(2 LEDs @ .38amp each + 3157 bulb turn signal element @ 2.1amp) .

The flasher fortuitously functions properly with this setup.
Perhaps other brands or designs of flashers may not work with this setup, but the Dodge OEM 5 pin flasher that came with the vehicle seems to function just fine.

Actually made use of the "extra" load light by drilling a hole and mounting the socket in a under the bed tool box.

Incidentally, the 3/4 inch mounting hole Trucklite Model 33 is the easiest mounting clearance light we have ever used.
Some the Model 33 clearance lights were mounted in 1-1/2" square tubing and had plenty of space to bend wiring.
The downside of the old stock Model 33 clearance light we used is they were not PC rated (*photometrically certified at installation angle) and we needed 2 lights at each corner of the flatbed. Trucklite recently began selling a PC rated Model 33 which can be mounted at a 45 degrees and one light at each corner will meet PC requirements..