What the best way to slightly lower the pitch on a spoken word vocal?

I think V-Vocal should do what you want.

Someone smarter than I will have to help with that. See if you can find some vids on working with v-vocal. It shouldn't go "glitchy" with a small adjustment. Maybe increase your buffer while it's processing? Again... beyond my knowledge base at this point. Good luck.

I know this is not the answer you want, but the IDEAL solution would be to do the transfer from the machine on which the recording was originally captured. You are hearing just the pitch difference, but - undoubtedly - there is a SPEED difference, as well (which, of course, is causing the higher pitch). Because cassette decks operated at such a slow speed, anyway, any variance in speed makes a noticeable difference. Small voltage differences could even cause that problem on the SAME machine.

Whenever I need to alter pitch, speed or both (which is actually what you need to do to get the recording back to its original state), I rely on a rather old version of Adobe Audition (v 1.5), but it also can create some nasty artifacts if you try to modify a file more than about 3-5% from its current speed/pitch. Audition 1.5 is kinda buggy running on Windows 7 (even in compatibility mode), and isn't available these days, anyway... so I am not sure I have been any help to you.

Try to learn the nuances of V-Vocal; within the Sonar environment, it is your best bet.

The lower I made the voice, the more glitchy it sounded.

The real time render for V-Vocal can sound glitchy, but if you bounce to clip (or do your final export) it uses a higher quality alg and most of the glitches will go.
 
Breath sounds and other noises that are "pitchless" can also confuse V-Vocal so if you're doing extreme pitch shifting they can sound like glitches, even though they're not.
 
"Beagle's Becan" in my sig uses extreme pitch shift on the main vocal, you can hear unshifted breath noise...

Melodyne will do a nice job. 

Someone mentioned the tape machine itself. This is true. I have seen several tape machines that had faster or slower tape speeds due to the motors or whatever. The original machine or one that tracks at the proper speed would be good to have. I believe there are machines with speed adjustments but they are typically more expensive and not widely available especially now that tape is not in wide use any more. 

I would not waste time on the machine approach.... get melodyne and get it done.

Give the old Cakewalk Pitch Shifter plug-in a try in the clip's fx bin.

In melodyne, you can "grab" (click and draw a box around them) the entire audio in the track by selecting it and move it a half step or so down in a matter of seconds. If you don't go too far down the formants should be OK.... I think the formants play a bigger part when going up. 

I moved a small steel guitar (polyphonic) part up a full octave yesterday, in a new project I'm working on, and all I did was select the entire clip and drag it up one octave ..... no formant adjustment and it sounded great. 

you might find the issue is with the tape recorder NOT the tape..  the rubber belt bands , loose shape over the years and due to that, also affect play back speed.  if you have changed the drive belts, again if they aren't the right size that will cause issue.

also the tape tension is ok ? (use a biro to fix that)


magic do some audio cleaning s/ware.. can't recall if it changes pitches though.. which if out are only out by a few cents/hz.


http://www.wavosaur.com is free and will do it.

in the tools menu will do pitch shift, and thats free.. IMO using melodyne etc is like using a sledge hammer to crack a walnut

The old destructive Pitch/Time plugin might be worth a look as well.   It's the one based on the MPEX algorithm (second tab).  You can preview the results to make sure they're acceptable - on a copy of the original clip, of course - and then process the whole thing... that could take a little bit depending on the length of the clip.   I've gotten decent results with it in the past before using VVocal and then Melodyne.  And it's one of the simpler methods since you key-in a negative pitch shift value.