While I typically over-maintain fluids, I'd say you are wasting your money by changing out the differential(s) and trans that early. With little city stop and go, you are very easy on your drivetrain.
You may see a 1 mpg or so increase in mpg due to less overall fluid friction in the differential(s) however that's certainly not worth the cost. Factory oil is not synthetic.
Edit - I was mistaken about the other fluids not being synthetic, another member said the diffs and transfer case were. I couldn't locate exact references to that however parts sources list synthetic so...
yYu can either:
1 - follow the FCA/RAM maintenance intervals for the "normal" or "severe" usage (if you want to be extra careful)
2 - go with a "gut" feeling of 50-70K miles on the differential(s) and same on the trans (no scientific or oil analysis information to back up that mileage interval though)
3 - just change it early cause' its your truck and you want to (look for specials/coupons to cushion the costs)
I tend to follow (1) "severe" but I only use conventional oils so it makes more sense to not stretch the intervals. It's a $64K retail truck so not worth it.
I doubt you could justify changing synthetic fluids very often unless you tow a lot or take the truck through water (streams). This is all my opinion of course.
Some RAM dealer has this online: (freeholddodge.net) which IMHO is a guide only. I'd disagree with the coolant, and would flush it as often as the tranny (for towing, not 120K).
Ram 1500 Service Intervals (freeholddodge)
- 8,000 Miles- During this service interval, the primary focus is changing out your oil and oil filter. During this time, you should also rotate your tires to even out the tread wear.
- 20,000 Miles- At this mileage, you'll want to have your front suspension, tie rod ends and brake linings inspected and possibly replaced if they don't meet the technician's standards.
- 30,000 Miles- When you hit this mileage, you'll want to have your CV/Universal joints, transfer fluid case and your front/rear axle surfaces inspected. You should also replace your engine air filter.
- 60,000 Miles- If you're using your Ram 1500 for a lot of trailering and towing, this is where you'll have your automatic transmission fluid and filters replaced.
- 100,000 Miles- At this service interval, on top of the many replacements and inspections, you'll have to add a few new items to the list. You'll need to have your spark plugs replaced. You'll also need your PCV valve inspected and possibly replaced.
- 120,000 Miles- If your Ram 1500 is equipped with a 6-speed automatic transmission, this is the point where you change out the fluid and filters. You'll also need to change the transfer fluid case.
- 150,000 Miles- During this service interval, you'll need to have your engine coolant flushed and replaced.
