Lights/Ground Problem

2005F150. It sat all winter while I was using my other truck, few days after I brought it back out
No brake lights, all rear lights dim on signal/hazard, all lights blink on signal even the license plate lights. Driver much brighter than pass.
Tried a different battery and all other lights on truck fine.
Went through all wiring from where it comes out of rocker panel all the way to the back, took off all grounds from frame cleaned and put back on. Nothing changed.
Anything else this could be? Not 100% but if the ground was closer to the front more systems would be flickering or not working.

Sounds like a typical ground problem, according to the wiring diagram, the ground wire for your tail/brake/turn and license lights is a black wire behind the left kick panel.

Fig. 40

The white wire you found at rear of truck is the ground for the trailer lights.
Fig. 41

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So I feel like ive done everything, went through everything, getting 12volts at all the lights and 12volts and at the ground so im not 100% where to go to from here, its my second truck so doubt ill take it somewhere, and just play with it when I think of anything else.
Any other ideas would be awesome cause i’m out.

Check the bulb sockets themselves for corrosion?

“even the license plate lights”? that should be a good point to trace with a voltmeter from that point back. if those are a switched ground circuit, you need to find where they are getting a ground. If it’s a switched hot, where they are getting 12 volts from.