I think 2d and 3nt should deny 5 spades; will this keep GIB from pulling 3nt to 4s?
In general I think GIB supports 2nd suits on 3 too often, like on auctions 1c-1s-2c-2h-3h; this shows only 3 hearts but I think it should have 4 normally. Supporting later can be on 3. It can bid Moysians based on sim, but it better be giving partner 4 cds in the suit not 5 when it sims.