spitfire

ok I'm new here so I'm looking for some help.
I've got an 89 truck and I just put a 95 motor in it, it's a 3.0 Sometimes when you start it ,it runs great other times it barley runs at all. If you turn it off and restart it two or three times it runs good again.
I just had it in the Toyota shop they put new plugs and wires ,but the problem remains, They suspect the key way on the crank might be sheared.
That doesn't make sence to me , wouldn't it run bad all the time since the timing would be off.
Not sure why it comes and goes like that any ideas would be helpful.