Wonky speedometer (96)

[St.rAnger96]

Hello - new to the forum. I've worked on a few Rangers and B's in the past but never owned one. Been a mech for about 15-20 years now, but my expertise is 50s-70s (mainly GM, sorry).
I just picked up a 96 xlt in decent shape and I've had an issue with the speedometer accuracy since I drove it home.

I have replaced the VSS twice now, and replace the connector as well. The plastic gear is perfect. Watching live data on my scanner I can see an accurate reading from the VSS, but the speedometer is about 10 mph off, when it isn't sticking.
(No codes, no flashing O/D, etc).

Two questions:
1.) should I just replace the speedo head and check the grounds along the way?
and...
2.) could this cause rough shifting? The 4r44e is both electronically controlled and fluid pressure controlled, correct?

Separate from the speedometer issue, I have replaced the #1 shift solenoid, the tcc solenoid, tightened the valve body to factory torque, fluid/filter change with fresh mercon v and a bottle of lubegard mercon v additive and adjusted both bands (appeared to have never been done).

I've done a lot of other maintenance to this so far that appeared to have never been done. U-joints, brakes, IAC, fuel pump, etc etc.

 

[St.rAnger96]

Confirmed with one of those speed trap warning signs that posts your MPH - I am exactly 10 UNDER what the speedo says.

Does this sound like just the speedo head? I don't wanna waste a morning and $100 if there's something else I should be looking into!

 

[Blmpkn]

Is the plastic gear the correct gear? I believe there's a handful of them available with different tooth counts for the end user to adjust for different tire sizes

 

[rusty ol ranger]

Wouldnt 96 have the speed sensor in the rear axle?

 

[St.rAnger96]

Wouldnt 96 have the speed sensor in the rear axle?

No that's an ABS sensor.

 

[St.rAnger96]

Is the plastic gear the correct gear? I believe there's a handful of them available with different tooth counts for the end user to adjust for different tire sizes

The gear is definitely stock to the truck. The VSS was the original blue anodized fomoco that looked ancient. Also, I changed from a 14 to a 15 inch rim with new tires and there was somehow... zero change in the way it reads. 10 mph off before and after the wheel change. Weird huh?

But also, regardless of the gear being the right one for the tire size - the speedometer still intermittently hangs in one spot before righting itself.