When I replaced my bulbs with the ones bassman has in his truck I also felt they weren’t bright enough.
I eventually replaced them with these bulbs:
Very little difference in brightness compared to the incandescent. Different look, which I was happy about, and a split second faster reaction time. They are pricey, but if you want a LED bulb back there, this is a bright as I have found. The forward firing LED is bright enough to fill out the lens and not look like a 1” light. The side firing LEDS reflect inside the chrome housing. The total effect fills out the tail light just like an incandescent would.
Interesting note: About a month ago, someone hit me from behind causing my truck to spin around several times before hitting a concrete wall in the front, side and back. Even though the back passenger tail light lens was missing and the back was pushed up to the tires, both LEDs in my tail light (brake and flasher) were still hanging from the sockets and working.