GIB saw the thread and decided to have a laugh. 1NT-2♦ 2♥-3♦ 4♦-4♥ (still the "5+♥, 4+♦, GF") From this point onward, I could do nothing to make GIB play in diamonds. Any number of diamonds was a cue bid and 4NT was RKCB for hearts. I thought it's counting on my doubleton heart at least, but it just had KTxxx so 6♦ was a much better contract. Its diamonds were T9xx which is what might've gotten him scared, but still, trust your partner (who happened to have ♦AKQJx, no joke)