I get the same song and dance when I go to the parts store. Seems dodge couldn't make up their minds which bulbs they wanted to use, so, the only sure way to know which ones are in your truck, is to pull 'em out and look.

As for the reverse lights, no idea there, but, I suspect I am going to get the chance to figure it out, as mine don't work.....

 

I looked the wiring up for my 96 and it shows a single filament bulb and only two wires going into the plug. So they are only using one of the filaments.

 

I've had the same reverse light bulbs in place in my 97' since the truck left the factory, so I checked today and they are indeed 3157 dual element bulbs. Same bulb as the Park/Turn signal/Brake light. Also both elements light up when the reverse lights are on.

 

Now thinking of it if the plug is for a single filament bulb and you put a duel filament bulb in it both will work. Seems strange the factory would do something like this rather then a single filament bulb. But maybe there weren't any bulbs that fit the application. ???

 

Seems perfectly reasonable to me. I would expect you want your backup lamps to be somewhat brighter than your running lamps...... the idea, after all, is to be able to see what's behind you. A single filament bulb may simply not put out enough light to do the job. Two, however, may be 'adequate'.

I need to figure out why my reverse lights don't work at all.......

 

I have the exact same thing on my '96 Ram 2500 4x4. I changed the tail light housings to LED recently and noticed backup bulb was a 3157 and both filaments come on when backing up. My backup lights are pretty bright.