HP Designjet z3200 PS Trouble Printing B&W Midtones

I'm having trouble printing B&W images. Specifically, midtones seems flat and pixelated. The file I am printing is a 16bit .psd file (300dpi). Printer has correct paper profile installed. Print settings are as follows:

Color Handling: Photoshop Manages Colors
Rendering Intent: Perceptual
Send 16-bit Data: checked
Color Options/Mode: Grayscale
Quality: Best
Maximum Detail: checked
More Passes: checked


Any help would be appreciated. A sample containing part of the image file vs the scanned print can be found here:
www.jasonproberts.com/clients/hp/printsample.tif

Thanks in advance!

 

Looks like the problem was the Grey/Gloss Enhancer printhead. Replaced and working fine.