I went to the parts store once to get a u joint for my 68 GMC. Told the guy I needed a u joint, told him the year, GMC 2wd half ton then he asked what motor does it have. I told him a 396. "well that's not factory motor, what did it have in it before?" that's the factory motor "no, GMC never put a 396 in a truck" I know they did b/c my grandpa bought it new from the dealer "he must have changed it at some point" I just had to turn around and leave. I can't believe they don't understand that sometimes their little computer might just be wrong.