Voltage (Mood) Swings

Hi all!
Second post ever on Forum and would appreciate insight...
2008 Tundra Crewmax SR5 with 196k. Recently noticed voltage gauge would dip and lights dim at idle only. Idle does not surge and remains steady. When I increase rpm beyond idle, problem disappears. I've replaced alternator with reman AC Delco from Rock, new serpentine belt and pulleys, along with MAF sensor due to code that tripped about same time as problem started. Problem continued despite these measures. Replaced battery cables...still no solution. Battery and alternator continue to test fine.

What am I missing? What's next?

I love this truck...not a lick of rust and does everything I ask of it (extremely well). Planning to drive it to a half million LOL...but this problem concerns me that I'll have a failure that may leave me stranded while towing in the white mountains!

 

When you replaced the battery cables, did you do the ground cable as well?

With a DC meter set to measure DC volts, what voltage do you measure with the truck idling between the battery negative post and the engine block? How about battery negative and the body?

 

Battery... if theyre not tighter than a virgin prisoner's ass cheeks, tighten both terminals.. if they're consider testing and or replacing the battery.. My optima did something like this before dying..