Question about starters
 

The original GMC V6 starter works OK for the 478 but cranks over a bit slow. As far as I know the 305/351 V6 always used a standard or low torque starter.

https://6066gmcclub.com/attachment.p...1&d=1758216551

I managed to score a Chevy high torque starter for cheap and was wanting to swap the high torque housing and rotor over and use the GMC V6 nose, resulting in a high torque starter for the V6.
But I ran into a problem. These is a difference in shaft length. This means I'd have to shorten the shaft and cut a new groove for the metal clip, which is doable.

https://6066gmcclub.com/attachment.p...1&d=1758216551

Another thing I'm wondering about is the length or the starter gear. As the GMC nose is much shorter, these is a lot less travel for the starter gear to engage, provided you're using the longer gear.
As you can see the gear that came off of the GMC starter is a lot shorter. Is this original? In the rebuild kits you always get a longer gear, and the Chevy starter is longer so you have plenty of linear travel. The longer gear in the GMC starter makes the gear almost contact the flywheel in its resting position, which is not ideal.

I can shorten the gear too, I'm just curious why the lengths of the shaft and the gear are not the same and if anybody else ran into these problems when they rebuilt their V6 starter.

Re: Question about starters
 

I realize you live overseas and shipping is way high along with whatever tariffs are doing. So maybe you sourced that Chevy starter there.

I believe this endeavor has too many issues to work. I know you are handy and quite knowledgeable in mechanical design. Me too. Whatever the correct GMC starter was used was good then and if refreshed will be good now.

Your issues, if I understand correctly, are quite likely:
1. Battery power, I.E. breaking down under load, need more amps, More CCA's, etc. Get a big CCA battery and make it fit the holder.
2. Corroded, dirty or loose cables.
3. Ground cable breakdown. Tripple check. Things get old or messed up in certain climates and don't get noticed.
4. Battery cable gauge too small. Get larger ga.

Don't know history of the issue, just started happening?, was good but gradual slower crank? truck won't start sometimes? crank speed faster at times and slower at times?......something new done to something?

A "bit" slow is good news. It means my list is the answer. All these "little" things will fix slow crank if starter motor is refreshed.

Stop before you screw up your only in-country GMC starter.

FYI: The power of a starter is in the number of field coils. 2, 3 or 4.

Anyway, this is my RSVP,
Willing to help. I know you are sleeping now. We are 9 hrs behind you.