I have a 1990 chevy k3500, srw, with 454 and three speed automatic. The trans has a 13 bolt pan. How do I tell if it's a th400, or a 3l80? I need to order a new trans, but am not sure which one I have. The rivited tag on the right side of trans says 90-DMA-2727. It also says DM 0018 A. I tried looking for a code on the teft side, but with an inch of gunk built up on the entire surface, and me laying in the snow trying to find a number, I feel helpless. There is no tv cable, so I figure the kickdown is electric. Any help on where exactly the stamped serial number is located, would give me a world of joy. Thanks in advance for your help.

 

A 400 and 3L80 are the same thing and if it's a three speed, that's what you have.


Allan