Manual transmission fluid for 1987 Chevy v20 6.2L Diesel with 4WD

[kcarrato]

Have a 1987 Chevy v20 with the 6.2L Diesel and 4WD and manual 4-speed transmission. Recently had the transmission fluid flushed and re-filled. Ever since it has been shifting very roughly. Mechanic used 75W-90 Full Synthetic. Indicated it would take awhile to break in but curious if that’s the right fluid for this transmission? Also, noticed that the fluid in the hydraulic clutch reservoir is quite brown so thinking I need to flush that and put new DOT3 in as well.

Anyone know what is best transmission fluid to use on this truck? I seem to find everything from AT fluid like Dexron II or III but also have seen full synthetic 75-90 suggested.

Welcome any insight.

Thanks

[More Power]

Your truck has the SM-465 manual 4-speed transmission.

The recommended lube is 85W-90 GL-4 rated lube, ~ 4 quarts per drain/fill if I remember correctly. If you live where it gets really cold, most use synthetic lube. If cold isn't a problem, I'd stick with what came in it from the factory - just a high quality non synthetic, mostly for oil seal compatibility.

Welcome to the board!

[spongebob]

same as your engine uses