What's the difference, on an automatic, between D4 & D3? I typicall drive in D4. The thing I heard was that D3 uses more gas but allows the car to accelerate better.
If you had a manual trans,
1 gear = D1
2 gear = D2
3 gear = D3
4 gear = D4
Now you would not want to drive around in 3rd gear would you, so what you heard is correct..
Would driving in third gear wear the engine or transmission (automatic, in this case) more easily or anything?
It would cause the engine to have to run at a higher rpm. That would use more fuel. and cause unnecessary wear on the engine. D3 is to provide more power for towing or steep uphill climbs. It's in your car manual.