What would be causing this?

[blackout51]

So lately my truck has been having a more buzzing type of vibration on top of the bad motor mount vibration, and when I shift to reverse and push the pedal the rpms drop to 450-500 then come back up before it moves, also when driving at night my lights inside and out dim when I let off the pedal for a second then return to normal brightness, not really a major problem I just am not sure what the cause is

 

[The_Roadie]

When was your last throttle body cleaning?

 

[blackout51]

When was your last throttle body cleaning?

Maybe two months ago I believe

 

[The_Roadie]

I was going to guess erratic idle RPM control, usually caused by a dirty throttle body. If not that, what's your mileage, and age of plugs? Vacuum leak?

 

[blackout51]

I was going to guess erratic idle RPM control, usually caused by a dirty throttle body. If not that, what's your mileage, and age of plugs? Vacuum leak?

Mileage is 137,xxx plugs are a few months old and are acdelco plugs, I've checked all over and can't find a vacuum leak unless its in the gasket but I figured it'd be acting up more and giving me lean codes if I had a vacuum leak

 

[CaptainXL]

Time to check cylinder compression