combining two standard leaf packs?

Hellow there TW

I find my self at a loss. I have hunted, crawled and poked my way through every part of the drive train looking for what has been giving me a "thunk" when I travel above 2,000rpm.

The scenario:
2,000rpm
let off the gas
Thunk
get back on gas
Thunk

I can't find a thing.
Carrier bearing looks good, 5 different shops say the u joints look good, trans mount is new, and I even have a brand new 4 leaf,leaf spring from Toyota on the back (warranty work).

I've narrowed it down to just plain ol' fashion Axle Wrap.

Thanks to a fellow Vermonter, I now have in my possession another stock leaf pack (43K miles on it)

I'm low on dollar bills, so...

Is it possible to take leafs from this extra leaf pack and slip them into my new stock leaf pack to increase rigidity and minimize the axle wrap I'm getting?