* TH350 3-speed automatic: This was a very common automatic transmission for many engine options.
* TH400 3-speed automatic: Also a possibility, though perhaps less frequent than the TH350.
* SM465 4-speed manual: A popular manual transmission option.
* 700R4 4-speed automatic overdrive: This became more common later in the 80s, so it's possible but less likely than the TH350 for an '86.
To know for certain what transmission was originally in *your* specific 1986 GMC Sierra 2WD, you need to check:
* The vehicle's build sheet (if available): This will definitively state the transmission.
* The VIN (Vehicle Identification Number): A decoding service can often tell you the transmission based on the VIN.
* The transmission itself: Look for markings on the transmission case – this is the least reliable method as transmissions could have been swapped.
Without more information about your specific truck, it's impossible to say definitively which transmission it originally had.
