'02 Astro with occasional strange gas smell when driving

Occasionally when we are out driving our '02 Astro with about 50K miles on it, we will start to smell this strange, maybe gas-like smell inside the van. Any ideas as to what is causing it? We smell it fairly frequently, but we haven't been able to pick up on a pattern of WHEN we smell it. We just bought this new-to-us van about 3 months ago. The smell is pretty strong, but then it goes away. It seems to happen whether we're driving at high speeds or even around the neighborhood, but it is only on occasion -- not all the time. Any ideas?

Is the Service Engine Soon light on? How does the engine run: any stalling, hesitation on acceleration, misfiring, etc?

No Service Engine Light or any other lights. Engine runs great. Only 50K miles on it. We just bought it a few months ago, and before we bought it, we had a mechanic check out everything. He didn't find any problems.

On occasion, the engine will sound like it's straining when it really isn't in a situation where it should be straining -- for ex., going for a drive through the neighborhood at 30 MPH and it has this muffled, straining sound like we're trying to gun it going up a hill or something. That also happens just on occasion, but we haven't seen a relation between that and the gas-like smell. I just want to make sure these aren't signs of trouble heading our way.

Possibly a problem with the fan clutch. When it has the straining sound, is it like a "roaring" sound from the engine compartment?

That would probably be a way to describe it. I'll have to check up on that. What do you think about the occasional, seemingly-unrelated gas smell when driving? Does that sound like anything to worry about?

There should never be a fuel smell, might want to have a shop look at both of those items.

had same occassional smell and turned out to be leaking fuel filter. Quick, inexpensive fix