Now about the other thing you said, are their shorter slip joints that will give me more room to slide or is this a driveshaft length issue?

Like I said before there is only maybe 1inch length difference with the new axle. Basically once the "new" axle was centered on the springs the drive yoke on the axle sits maybe 1in further forward maximum then the original rear axles drive yoke. And this is what took my extra sliding room for driveshaft away.

And I know of a guy who owns 60acres of these medium duty trucks that he started collecting as a salvage yard. So I can probably find different length driveshafts or slip joints I'm sure on one of the many trucks he has if they made these in slightly different lengths, like what I would need to get more sliding room. But did they actually make these parts in 1inch length differences???