The cargo's and the 3rd/high mounted brake light between them. (They are all 921 bulbs.)
I just re-gained access to my photo account, took a while since I made it just for this forum and I was away for a few years. I'll try to get some before & after photos up this week but I think it's supposed to rain.

I only see one option I would try from the same vendor (who seems to be pretty highly rated & they did respond fairly fast to an email I wrote them.) for the tails - $30 for the pair: 3157 (No 3057's listed in search).

While we're talking rear exterior lights...
For the reverse lights I plan to try these 3157's as I live in a somewhat country area and could use the extra light backing up to my barn/etc. $20 pair: 3157
Finally, the license plate bulbs $7 pair: 168 (Lot's of 168 options available, these are the cheapest with the right SMD layout, plus) first review is on a Ram.)

 

I look forward to the photos when you post them.

I've considered tail lights; I'd be interested in your review of them, if you get them. I don't recall exactly, but it seems like the difference between 3157 and 3057 had to do with the ability to get brighter when the brakes are applied. One did and the other didn't...or something like that.

Better back-up lights would be great. I'm not sure that I care about the license plate light, though.

 

Apologies for the delay.

First up is the 3rd brake light. Honestly the brightness difference in the OEM housing for some reason isn't massive, they are brighter but if nothing else changed I'd say replace the halogen with LED whenever yours burns out. However, I did notice when my wife hit the brakes at the end of the driveway they activated MUCH faster than my halogen tail lights. So I'd recommend only replacing if you get a benefit from the extra second faster notification to your tailgaters, if you're more of a country road scene YMMV but technically LED helps your gas mileage by like 0.01% so yeah...

In full disclosure: the before photos are in a junkyard 2005 lens that I pulled from a yard which wasn't much better than my stock one & the after photos are in dakotaff's OEM lens I bought which are less cloudy as they have been in a box since July 2011. This let me do before and after photos just before sunset for decent light examples while allowing me to change them out quickly enough to avoid a big natural light change. This was more helpful for the 3rd brake light. The cargo's are a huge difference.

Before:


After:


Next up are the cargo's, wish I had done these years ago! MUCH better light output in the bed and far beyond.

Before:


After:


Also Amazon suggested new gasket & I went for it. I think it was worth it, the new one is at the bottom:

 

I'm pretty sure I'll get them but it might be a month or so, I've been checking out Dakotas for sale lately, looking for one with less rust but the high end tow rating and of course less miles if I can. So I might as well wait and see if I can put them in the next "new to me" one. I actually was going to trade in our car and put $500 down on a custom order GMC Canyon Diesel 4x4 Long Bed Saturday and got my $ back today because they are ordered out of 2019 Diesel engines... I guess it's a sign.

I understand your point on the license plate lights. I'm planning to do them for 3 reasons:

1. I often find myself loading firewood & materials after dark with the tailgate down, with the new cargo's that shadow under the tailgate has only become worse, I think this will be enough to close the gap without spending much cash.
2. These are on the moment you turn on your parking lights continuously until you turn off the key, so this is a location that actually might make a more significant impact on MPG, and I don't know about you but my MPG's are in the teens and I'm working on doing heated mirrors and seats which won't help, plus I'm running the H.O. motor which is nice but wants 91 octane, maybe this will offset?
3. I don't do much for vanity but now at night when I tap the unlock button the cargo lights make the halogens look dingy...

 

Gasket looks like it was a good call. Your truck looks like it has seen some living and working. Which spray-on bedliner did you get? It looks like it is holding up pretty well.

The cargo lamps are really bright! They look like they were definitely worth the money and effort. The taillights are brighter, but I don't know about the "instant on" being worth the money. I figure that if you're following me that closely, then you must be confident that you're ready to buy me a new truck when you hit me. The one caution I've seen for LED taillights is to ensure that there is a very distinct difference between the brightness of the running light and the brake light. That seems to be more important than how quickly the light comes on. So, on that note, how dramatic is the difference between the taillights just being on and when the brake peddle is pressed?

I don't know about brighter vanity lights. I like the dimmer lights because my night vision recovers faster when the vanity lights aren't too bright. But, I'm guessing the difference in the halogen and LED back-up lights will be similar to your cargo lights.

I don't think you'll save any MPG with LEDs. I have the V8 Magnum and I'm also in the mid-teens for MPG. My only advantage over the HO is that my Magnum uses 87 octane and still gets better hp and torque. I don't think the amperage draw on the halogens was enough to make much difference on the MPGs. So, reducing the draw for the LEDs is probably only a negligible effect on the MPG. Just a guess... To me, the LEDs are upgrades for brightness, or color in the case of headlights.

 

Oh yes it's been through a lot, built a barn, remodeled my old house, a few commercial construction sites, some roadside communication line repairs, several hunting trips & have towed a camper I had from 2013-2018 along with a small boat, my 12x16' flatbed trailer with short sides full of wood way too many times to count & once my the old Pontiac we just traded in due to flat not far from Tire shop on the highway (was safer to just load it up and tow it ~10 miles & let them warranty fix the tire for free.) plus rental bobcat's & tree chippers. Oh yea then there was the time I towed my father in-law's ranger back from Oklahoma... Anyway LineX is what I got in 2011, over my passenger wheel it's helping the rust hold hands or I'd have an unwanted vent. The white spots are where the aluminum rack mount points were for years, I took that off (2018?) after I moved to the new place after I got the trailer since I have a place to park one now. Here is the thread I did that shows when I got those installed.

I only changed out the top/3rd brake bulb, the tails only look brighter since it was darker outside and I think I was standing closer? I donno maybe I pushed the brick harder the second time...
The 3rd light is off until you press the brake so besides faster it is a brighter difference but it wasn't much brighter in my case for some reason.

The manufactures are starting to go LED to help meet the more stringent MPG requirements but it's not like they will pay for themselves, it will just help a sprinkle if you like the other reasons to do it.