Exterior and interior lights flickering

Okay, so the lights were flickering and you swapped alternators and still have a flicker.

Which lights? Headlights? tail lights? dash lights? all the above?
Is there a pattern to the flicker? Like hit a bump and it gets worse? Or turn on the headlights and it's worse? Turn signals?
Do the lights flicker if you turn them on with the engine off?
Do they get brighter if you start the engine with them on?
Any change if you wiggle the dimmer switch or the light switch?

I suspect you have a bad connection either at the headlight switch or the power feed side. The answers to the above should help narrow that down.

Sorry I had to edit my reply. which is after this message ironically.

Well all my exterior and interior lights flicker. Every one of them. They do not flicker when the truck engine is off though. So far, the only things that I notice is. Sometimes the flickering is not as bad as other times. The weird thing is when you unplug the alternator, the flickering stops. I am not sure if what I am about to say has to do with the problem with all the lights flickering but sometimes my engine runs a little rough. And sometimes that happens with the flickering. Also, when I am parked and the engine is on, if I raise the engine rpm to around 4000, the speedometer moves to around twenty mph and I am not moving! Very weird.

Okay no flicker with the engine off, but flicker with it running. Unplugging the alternator would switch the lights onto nice clean steady battery power.

All of this suggests that you have a bad cable or connection in the charging system. Engine motion moves the wiring enough that it interrupts the power and the lights flicker as the voltage changes. Start by looking at the connections at the alternator. Turn the lights on with the engine running and wiggle the wiring on the alternator and around it. Especially the one that feeds the battery to charge it. They can corrode inside the terminals and still look perfect. Also check the ground side as well from the battery to the engine and body.

Well to continue from our conversations earlier on here, every one of my exterior and interior lights flicker, still. Like I said, I tried many different new re-manufactured alternators. currently I have a new re-manufactured Ford Motorcraft one in my truck listed above it is the xlt fx4 level II model. My dad and I replaced the ground plug on the alternator and the main bigger plug too on the alternator. The lights are still flickering. And I think my engine runs a little rough also. We did notice my belt tension-er moves when the engine is running. The tension-er is located right below the alternator and it is connected to the same big belt that is also connected to the alternator. It is kind of like the belt tension-er flaps around (moving) while spinning. Could that be the cause?