Needing advice...
Usually if you read backlash before taking the gears out of the original rear, and setting the new one up exactly the same it won't make any noise at all.
Another problem I hear of often is how people think the original GM pinion shim is close enough. I read that a lot when people put in new aftermarket gears, many recommend starting with the original shim. They come in a variety of thicknesses for a reason.
The shim matches the rear housing and pinion both. Not one or the other. The factory selects the shim based on case intolerances and pinion machining indifferences. Change only one and that shim is useless, and you changed both by putting a different pinion in a different case.
And there is no way to set up a used gear set with any special tool, all you need is marking compound and a shim kit, it's trial and error until the pattern is right.
If it's not dead on it's going to make noise, gears don't break in again. You don't set a new wear pattern on gears twice.
Sounds like they got the pattern close enough, and used a tried a true excuse.
Where does the GM Phoenix cut fit in? What cut is that? The Phoenix cut is the one with the different pattern.


