In a 99 ford ranger 3.0 V6 2WD what gear oil do you put in a manual transmission and in your rear differential?

I would use a Synthetic Extreme Pressure (EP) Lubricant 75W-90 (SVG) in your rear differential,
In the Transmission a 5W-30 Synthetic Synchromesh Transmission Fluid (MTF).
Normal ATF is about 5W-20. 1991-current Rangers with the 3.0 engine:
The [http://www.therangerstation.com/tech_library/pdf_documents/ToyoKoygoMazda.pdf Mazda M5OD-R1] is the only manual transmission used in Rangers with this engine. Mazda R-1 5-Speed Code "M" This is a top shift fully synchronized transmission. This has a light duty aluminum case and has a rectangular shape casting ribs with a large top cover. The R-2 is known for leaking oil from a rubber plug in the top cover. You should replace the rubber plug with a steel Dorman cup plug PN# 555-108 or Dana PN#219-3052. You will need 3 plugs. These trannies often melt down due to the oil loss caused by these plugs. Many owners have went with synthetic transmission fluid hoping to extend the life of the transmission. Synthetic fluid handles high temperatures and pressures better then conventional fluids. The hydraulic clutch, slave cylinder/throwout bearing is another item you should pay close attention to. After time, the slave cylinder fails to release the clutch completely. If you are having trouble shifting into 1st and reverse while stationary or if your truck creeps forward with the clutch pedal depressed the slave cylinder/throwout bearing is probably at fault. Unfortunately there is no easy fix here as the transmission must be removed to replace the combination slave cylinder and throwout bearing. [http://www.therangerstation.com/tech_library/ManualTransmission.html Source]
Also here are the Fluid Capicites for your Truck. Hope they help. CAPACITIES
Engine, with filter..........4.6 quarts[1]
Cooling System, Initial Fill..........15.0 quarts
Automatic Transmission, Initial Fill..........3.9 quarts[2]
Automatic Transmission, Total Fill
4R44E..........9.9 quarts
2wd 5R55E..........10.0 quarts
4wd 5R55E..........10.0 quarts
Manual Transmission, M5OD..........5.5 pints
Differential, Front..........3.6 pints
Differential, Rear..........5.1 pints[3]
Transfer Case,Warner 1354..........2.5 pints
Transfer Case,Warner Others..........3.0 pints
1. When refilling, remove dipstick to provide adequate venting and allow oil to flow into crankcase.
2. With ENG at operating temperature, shift through all gears. Check fluid level in PARK and add fluid as needed.
3. Fill to no more than 1/4 to 9/16" below fill plug hole. Good Luck and Remember.
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