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**hatzie** · 07-11-2011, 08:30 PM

The RPO M40 on your SPID is for a TH400.
If your SPID tag said M38 it would be a TH350.
The 4L60/TH700R4 was not available in 1975 but the RPO is MD8.

Your truck is 36 years old so anything could be installed now.

chevy-transmission-identification

07-11-2011, 08:30 PM	#5
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 5,020	Re: Transmission Identification The RPO M40 on your SPID is for a TH400. If your SPID tag said M38 it would be a TH350. The 4L60/TH700R4 was not available in 1975 but the RPO is MD8. Your truck is 36 years old so anything could be installed now. chevy-transmission-identification