1994 Isuzu Rodeo Question timing belt

Gentlemen,
I can't figure this one out. My timing belt slipped a few teeth and wouldn't start. I put on a new water pump, a new belt tensioner, a new iming belt and replaced all the outside belts. A few weeks later, I pulled in to my driveway and shutoff the car. Ten minutes later, I returned and tried to start the car- no go. The timing belt slipped again and wouldn't start. This has happened 3 times since I replaced every thing. I getting real good at pulling everything off and putting it back together. But, I sure would like to find out why it's doing this. I checked out the teeth on both cam sprockets and the crank gear. They look okay to me. Any clue as to what is happening?
Chuck