I used a very LARGE strap wrench with a wide canvas belt and long handle.(RIGID makes these) I could see that there was red locktite on the threads and nut face. I don't know if this was put on at the factory or the previous owner did this. It had the stock 3.4" pulley and looked like brand new with under 4K miles. Because I have elec. fans, I was able to stand inside the engine bay and position myself over the wrenches for max. torque(grunting). You may want to remove your fan and shroud to try this same thing. Don't think I could have applied enough torque without doing this.
Good Luck.

 

appreciate all the input guys...I guess I am just going to try and muscle it a little more. I like the "old belt" and channel lock idea. My pride is a little hurt as bench pressing 400+ lbs is no problem, but I can't get a damn 18 mm nut off a shaft

 

Yep Thats exactly what I did I think I even tore a belt or 2 before finally getting it just stay patient and get it done youre gonna love that 2.9 pulley.

 

This is what I recommended after my belt wrench wouldn't hold it. Don't know whats going on with this one.... It's specially tight. I didn't have a pair of channel locks large enough.

 

This worked like a charm...came right off! The truck is A LOT more fun now too Only thing is now the damn belt is sqeaking like crazy......???

 

Smaller pulley requires a smaller belt.....

 

makes sense....I was just assuming that the tensioner would take care of that...??
And it feels so tight I can't imagine it being any tighter.

 

You've got the new adjustable type idler on that one. Might be able to tighten it up a bit.