gas in the oil of my 99 crown vic

I recently purchased a non-police, 99 vic with 146k miles. it has 3 issues I can't figure out, first is, after I fill the car with gas, it is very hard to start for the first time, once it starts, it runs very rough for a moment, then smooth's out. the second is a strong fuel smell on the dip stick when I check the oil. fuel mileage is weak, 10 mpg in town, the last thing is, from a cold start it fires, then bogs down for a second or two then smooth's out. any help out there for these issues? I took it to have any codes pulled and there are none, I thought the first place screwed up so I took it to a second place with the same result.

Make sure the gas cap is on correctly and venting properly.