What type of transmission does a 1992 Chevy G 20 with V8 have?

A 1992 Chevy G20 van with a V8 engine most likely had a TH400 3-speed automatic transmission or, less commonly, a 4L60E 4-speed automatic transmission. The specific transmission would depend on the exact trim level and options selected when the van was new. Checking the vehicle's identification number (VIN) or looking at the transmission itself would be the best way to know for sure.