Bizarre behavior 1998 s90

[mplishka]

So here's the situation. When the car is being driven over 60 miles an hour and it seems like it's warmer out or the engine has been running for a while, it starts hesitating at high speed.
But, This is the weird thing. I can tell if it's going to hesitate when I start the car. If it takes more than a couple seconds of cranking before the car turns over, I know when I get to the highway it's going to hesitate at high speeds. If it starts normal, within a second or so of turning the key, I won't have a problem. We've had screwy Spring weather but it seems like this problem shows its head when the outdoor temperature is above 60 degrees but that could be coincidemce.
Oh, and none of this happened when I had a loose engine oil cap that was spattering oil. After replacing the cap, this all started. Coincidence?

Any thoughts?

recently replaced the plastic molded air intake boot by the throttle because it had a huge crack in it, I thought that might solve it oh, but it didn't.
thanks!!

[manyvolvosmoveme]

This is making me think the fuel pump is going out. Turn the key and hold just for a second before engaging the starter. If that gives the pump a moment to prime and it always starts right up but if you don't give it a moment and it turns over for longer than normal, i would think fuel pump. As for when you are driving, same thing. Are you going up a hill, accelerating, did the A/C just kick on?