Graber i3 variant, problems of z axis friction?

Hi guys,
I built myself a graber i3 variation, and the z axis is making me crazy. Almost everything works fine, but the z axis. It's basically always grinding, like motors don't have enough torque to overcome static friction (once it starts rotating it's almost fine for a time). e.g. I completed a print of a spiral vase keepin my hands on the motor axis and helping it when I feel skipped steps. Threaded rods are M5, and I think they are badly bent. I don't think I can get unbent rods, especially at these sizes, I feel like M5 bends when you look at it. I'd buy a new one, and bend it when I cut it, and be back at square 1

What's the next step in diagnosing and solving that problem?

Solved my problem, OK bye. Just kidding. The problem was of course the bent rods. And my stubborness to have 2 nut traps on each carriage on the z axis, bad bad idea (it's overconstraining the assembly, that could still work but would require very straight rods). I removed the bottom one, enlarged the holes so that the rods can wobble a bit, pushed the vref on the z axis drivers a bit, and no grinding anymore.
Although no one answered it, I'll put my solutio here in case anyone stumbles on the same self-created problem.
Cheers

Not sure what type of board you have, but I think it would be good idea to add a dedicated fan to cool ALL stepper drivers... No matter how cool they are....
My cent

Glad you fix the issue...
Some time is just that, we came up with question, and we solve them ourself and share that experience out laud, so others, would benefit in the future!,

Good post and keep doing!
Good print!