Just out of curiosity, how much did they charge for doing both differentials and the transfer case? I would guess $250?
I just did all three recently with Mobil 1 and Mopar friction modifier in the diffs and Mopar fluid in the transfer case, and it cost me about $120 for the fluids and $0 for labor.
I like using the synthetics when possible. I also like cracking open the rear diff rather than just sucking out the fluid. You get a better flavor of how it is doing.
'06 XK Limited, 5.7L, QD II, Black, 163K
'02 WJ Overland, 4.7L HO, QD, Inferno Red, 126K