Can you change from ATF to 30weight for your transfer case?I am a big fan of changing out the intial fluids when a vehicle is new; doing the diffs and t-case around 10k miles can't be harmful, and helps flush out an manufacturing remnants. After that, though, the intervals can well be extended to at least 50k miles, and sometimes more, depending upon service severity and fluid used. Don't confuse change intervals with service intervals. You might only have to change fluids every 50k miles, but you should check the level every 10-15k miles.
As a massive generalization, you can do the changes yourself and save yourself a huge amount of money. $340 is grossly overpriced.
Here's a rundown of the must-do and should-consider topics:
Diffs - must use a GL-5 rated diff fluid with the low end of the grade around 75w (or 80w), and the high end from 90 to 140 grade; all depending upon service severity and length. "Synthetic" fluids are NOT required; they are recommended - you'll get longer service life out of them. Just about any brand will suffice, but a recent test from Amsoil showed their Severe Gear to be tops, with the Mobil 1 fluid a close second. All others were not that competitive, and fell back fairly substantially. Brand wars aside, the paper was well written, well documented, and (while sponsored by Amsoil) not entirely biased. The proper stated capacity is 2 qts in front diff, and 4 qts in the rear diff.
For t-case fluid, there's a large controversy over this. I believe the proper fluid is ATF fluid based upon (former) DEX/Mercon base stock chemistry; that's what the t-case was designed for. If you choose to "upgrade" you can use s "synthetic" ATF from one of many sources. Other people choose to use 5w-30 synthetic motor oil. There was an article written by Rockland about how the motor oil supposedly resisted evaporation better; a case of mistaken facts and little understanding of tribology. However, there is no proof that motor oil either helps or hurts the t-case. I prefer to use the factory spec'd fluid in the t-case; others don't. To each his own. There is plenty of factual basis for using the ATF; there is none other than anticdotal evidence for the motor oil; choose as you see fit. Further, those that use motor oil often overfill the t-case by 50%. The stated capacity is 2 quarts; the overfill takes 3 quarts total. Again, choose as you see fit. There is no proof that the overfilling helps anything.
What is known to "help" is proper maintenance with proper fluids. Change your fluids on a regular, reasonable basis and you'll have a vehicle that lasts a long, long time.