have a problem matching the shade of text in merge fields to the pdf in the static part of variable data letters. the pdf text is always a lighter shade than the psmail variable text. we can shade the text slightly but it pixelates.

I believe you have a few options , or reasons for this happening.
1) If you are working directly in CMYK - in both the PDF and PSM, then I think you may have an embedded colour profile changing the colour in the PDF at RIP stage - depending on the Rip there is usually a setting to remove any embedded colour profiles.
2) If you have a spot or PMS colour in the PDF, then I would suggest also creating a spot in PSM (V6) (with exactly the same name), then allowing the RIP to do a look up and replace of that named colour - overriding any colour profiles, should give you the same colour when output in both the static PDF and variable PSM content.
3) You could also use a program such as Pitstop to adjust the PDF colour directly in Acrobat - however, again if you save with colour profiles the colour will change when printed.
4) You could also read the section in the PSM help (V6) about colour profiles - which can be enabled under preferences.

Hope this helps.

it's just the black font - not colors - the pdf is always lighter than the merge fields of text.

Black is also affected by color profiles and color management settings.

Would you be able to send some sample files to support@printshopmail.com so we can take a look at it here? We won't be able to determine the color settings of your RIP, and we probably won't be able to see the settings of your printer driver, but at least it will allow us to see which colorspaces you're using, whether color management in PSM is enabled, how the PDF is set up, etc.