2nd place too many times

[Hung]

Hello,

I play a lot of sit and go's on party. $100 or $200 NL HE tables. I also bought poker tracker not so long ago. I have 54 sit and go's in my PT database. 30% of the times I get 2nd place. I only got 1st place 4 times. Somehow I always lose when we're HU. They call with incredible things. For example, today. I have 3k in chips and he has 7k in chips. He's sb and I'm bb. Blinds are 250-500. He calls and I move all-in. He calls with 45o and wins with pair of 5. I ran the odds in some poker prgram. K7 beats 45o 62% of the time. That does not seem a lot to me. That means you'll lose 4 out of ten times. I also make a lot of moves when I have an ace or any pair. But they never seem to hold. Eventhough I'm holding a stronger hand. THe blinds are very high and you can't wait for big hands. Any two face cards, pairs or aces has to be played. Yesterday I ran into AA twice in a headsup situation. He got AA twice.
Another guy raised chip with 79s UTG (blinds 100-200) and I moved all in with AKo (I have a bigger stack) He calls and flops a straight. I'm still in the tournament. But WTF? I'm not talking about idiots, I see these guys play several sit and go's. So they're not morons, trying a sit & go.
I need to change my strategy. I think it's weird that a higker card has such a weak value in HU situation.