Houston rear diff rebuild?

OK - so, my recent T56 swap, along with 4.09 FRPP gear set/FRPP install kit...the guy who did the install didn't do it right, and isn't willing to stand behind his work. So, I'm just screwed on that deal...massive vibration was caused by a loose pinion nut...dude tightened it up, but, here we are again, same problem is back.

I probably will need to purchase the 4.09 gear/install kit AGAIN...

I need to find a good reputable shop who will stand behind their work, and fix this thing correctly.

Any suggestions in the Houston area?

Nothing special about the R&P setup in our cars. Any reputable drivetrain shop should be able to do it easily.
How about these guys - https://houstondrivetrain.com/service.html