I think you made various mistakes on this hand, one of them is a classical blunder.
The classical blunder is: don't inquire for keycards prematurely, especially with a telling hand. When you are slamming, you have to ask yourself: do I have a telling hand or an asking hand? An asking hand has got something that really cannot be explained in the bidding (some freak distribution), so you must go and find out as much as possible about partner (ask partner). If you have a telling hand, you have values that can easily be relayed by cuebidding or responding to keycard inquiries (tell partner).
When your partner told you that he was 5/5 and strong (I play it the same, but in my case it is GF), you lost control of the auction by ASKING, when you had to be TELLING.
Your correct bid after 3C is 4C. You have excellent support for his club suit. Not only, that, you set the perfect pace for cuebids, because after partner's expected 4D, you can bid 4S, showing you have no support in hearts. Partner will know what to do. He can inquire with 4NT and if he signs off after your 5H, you know a keycard is missing. If he does a try for grand, you have an easy 7C with your spade suit and Kd.
After 4C reaching the grand slam isn't difficult.If you play RKC Lackwood (Exclusion RKC), partner can bid 5D, you reply 5NT (2 keycards)-7C.
If you don't play Exclusion RKC, you can still get there:
1H-1S
3C-4C
4D-4S
5D-5NT
7C.
Partner's 5D bid is a grand slam try, he has heard you skipping hearts, so he must have first control in both red suits. With your solid spade suit, all you need to know is AQc and you use Josephine GSF to find out.
Cliffs: Instead of taking control in a spot where you end up not knowing what to do, do it the other way and put your partner in a spot where he knows exactly what to do.
Last edited by Gabethebabe; 10-08-2019 at 02:30 AM.