Before, of course; adults rarely take IQ tests, though it would be interesting to know his GMAT scores [actually, those were only another 5 years later]. The two known scores are his SATs and his military tests. As Sailer (last link) always says,

the only election Bush ever lost was a 1978 Congressional race in the Texas Panhandle, where his opponent made fun of Bush for having degrees from Yale and Harvard.

Bush resolved never to get out-dumbed again.

ETA: my impression, probably from [the video James Andrix cites below], is that Bush sounded much more coherent during the gubernatorial elections than during the presidential ones, which would rule out a direct effect of alcohol.