Test with the engine running. So you know you're getting full voltage to everything. So - only the outside cap lights are dim? The other outside marker lights are full brightness? If so, that's a bit odd.
For the tailight that's partly working - you need a helper. Figure out what's out. Running lights, brake light, reverse?
Pop the cover off the bad taillight, turn the lights on and if you have a voltmeter, check for voltage. LEDs do fail, but failure for quality ones are rare. But -- quality and Jayco seems to be at odds these days.
You may need the helper to step on the brake, or pop it into reverse. If there's voltage going to the part of the LED that's out, then you know to replace the fixture.
Some rear-taillight assemblies have separate "bulbs". Other cheaper ones are "all in one" - there's no way to easily replace the lights that are out and you have to buy a new fixture.
As for the dim cap over-cab lights, I'm thinking you're going to have to go up there and dig into them. Another idea for Creative Debugging would be to buy a simple. cheap, LED marker light from Walmart. Like $5. Just any old LED light.
Climb up, remove the old cap light, wire in the Walmart one and see if it's bright or dim... Dim? We've got a voltage or ground problem. Bright? Time for a new light fixture.
What I'm suggesting is that you figure out what's going on before buying new bulbs or assemblies. Would be a bummer to buy replacement fixtures only to have those also be dim...