HP2600dn lineweights not thin

We purchased an HP2600dn (Feb '04) shipped with the current firmware and drivers. The printer and JetDirect software are installed on a Windows NT4 server. Our AutoCAD workstation runs Windows 2000 SP4 and AutoCAD 2002 SP1. We plot to the network printer using the PCL 5C driver out to 11x17 paper in landscape

The HP2600dn was a replacement for an older HP1220C, which (when it worked) plotted the lightweight lines beautifully (PC3 driver). Now, the weights for lines less than about 0.25mm cannot be distinguished. We often use lightweight lines, so this is a problem. HP support has deflected this issue as a problem with AutoCAD.

I can get the desired quality with the PCL5 driver when I configure a plot style with best print quality; raster mode; and, line merge. However, the job takes an unreasonably long time to complete.

I’ve tried other settings for the PCL5 driver (automatic or vector graphics modes; line overwrite), but the minimum plotted lineweight is always too thick. Also, the drawing is plotted with a very slight lateral shift every 31/32†in the long direction, making horizontal lines appear choppy. (This shift also occurred every 31/32†when plotting on 8.5x11 paper.) Using the PS driver, the light lines were a little cleaner but the heavy lines were much heavier and the text printed as though it were bold.

Any solutions for how to plot the lineweights correctly and quickly?