I agree 100% with Reed; he's right on target, and perhaps this is what the root of the issue with your getting good readings has been. -There's no three positions forward!
You'd mentioned having thought there might be some wear in your ignition switch, and that you replaced the (electrical) ignition switch assembly itself. You and I have both done that. But due to vague feeling switch detents, I also replaced the lock cylinder and some of the drive mechanism which the cylinder moves, such as the rack and sector gears. The key switch stop positions became much better defined and repeatable after that.
That being said, even the FSM says that the "lock" position is the most positively defined in location.
I've been suspicious of your ignition switch assembly possibly requiring some refinement to its adjustment after the replacement, or of its actuator rod being bent, but I hadn't caught onto the wear in your lock cylinder and drive mechanism being so substantial.
I think you might benefit substantially from replacing your lock cylinder. They're not expensive at all, $15-20, and they come with brand new keys. (Melanie would be thrilled...)
This eliminates wear of the keys and of the tumblers as sources of trouble.
You could also clean up the rack and sector gears and decide if they warrant any further action. I'm sure that at the very least they'd benefit from a refreshing of their 30 year old lubricant!!
In case you should need it, due to damage to the gears such as chipped or worn teeth, here's your secret weapon - the "Rack Package". This is what I got in addition to the lock cylinder, and these kits are still in stock (-will wonders never cease!!) ;) at Chrysler dealers.
Chrysler part #4147364 - Rack package
PARTS: Rack package includes rack, bearing, sector and spring.
At
http://www.wholesalemopar.com/parts_catalog.html these kits show up for $55.
Here's a decent picture of what's in the kit:
http://www.amazon.com/Steering-Column-Tilt-Bearing-Rack/dp/B00ADWKEXIYou may need to borrow a steering wheel puller from an auto parts store to make the job practical, but I'm certain you wouldn't find the replacement to be overly challenging. The hardest part might actually be trying to squint hard enough to make out the details in the illustrations in the FSM!
Here's a bunch of videos of the various processes:
http://www.steeringcolumnservices.c.../GM-Tilt-Column-Rebuild-Instructions.phpAnd a couple of very detailed descriptions, including the procedure for adjusting the ignition switch assy:
http://www.crankshaftcoalition.com/wiki/images/d/d6/Jazzman_Steering_Rack_Rebuild.pdfhttp://vintage.mitchell1.com/PClubData/chassis/dch82/V2D8212017.pdfOne other potentially useful tip on the Dodge van steering columns; standard steering columns were made by Chrysler, while tilt steering columns were made by Saginaw. Saginaw columns appeared in numerous other vehicles, not all of which were Dodge! The reason I point this out is that if Chrysler dealers belch out their typical well-rehearsed refrain of "no longer available", there may still be plenty of other sources elsewhere for parts. A GM dealer for instance...