how necessary is the following: differential flush, coolant fluid exchange, fuel injection service, and if so, when.
If you are planning on keeping your vehicle and want to cut down on repairs, then changing fluids and maintaining your vehicle is the best way to do so. your owner’s manual will tell you what and when to change it.
If not listed in the maintenance schedule, those are “up-sells”.
Coolant drain and fill is scheduled at 10 years/100,000 miles.
Differential drain and fill every 30,000 miles is necessary for special operating conditions: towing, heavy loads, driving in water.
No experience w/your vehicle, but I own on older Ford truck, driven gently over the years, what I do might provide some insight at least.
differential flush … I do that every 20-50K, but expect it could go a bit longer. Usually the impetus for the fluid refresh is the seal starts leaking. Some differentials (like mine) require an friction modifier additive to the replaced gear oil, so double check if that applies to your Tacoma. If I ever cross steams, where the water is high enough to reach the differential, I replace the differential fluid within a few days.
coolant fluid exchange, I replace the truck’s coolant every 20-30K miles, or 3 years. Coolant looks to be in pretty good shape at that interval, but more frequent replacement seems to extend the life of the water pump.
fuel injection service, my truck has a carburetor, not fuel injected. Other than lubing the linkages, I don’t do anything proactive service for it (other than replacing the fuel filter per schedule), just repair if/when it develops a problem. I don’t do any proactive fuel injection service for my fuel-injected Corolla either, other than replacing the fuel filter at the specified intervals. If there’s any indication of fuel injector problems, happens rarely, I’ll put some fuel injector cleaner in the gas tank.
The shop could be going by the MAP (Motorist Assurance Program) standards…
Beware the fluid flush scam. Avoid The Vehicle Fluid Flush Scam - Car Talk