* TH700-R4 3-speed automatic: This was a very common automatic transmission in many GM vehicles of that era.
* SM465 4-speed manual: A robust manual transmission also frequently found in these vans.
* 4L60-E 4-speed automatic: Less common, but possible depending on the specific options.
To know for certain what transmission is in a *specific* 1990 Chevy G20 van, you'd need to check the vehicle's:
* Vehicle Identification Number (VIN): A decoder can often tell you the transmission code.
* Build sheet (if available): This document will specify the options chosen, including the transmission.
* The transmission itself: Looking at the transmission case may reveal identifying numbers or markings.
Without more specific information about that particular van, it's impossible to say definitively.
