1998 Ford Expedition P0171 P0174 trouble codes, check engine on, failed smog. HELP?

I have been researching online and asked a couple of mechanics on what to do to pinpoint the problem with my truck, im a bit newbie when it comes to cars but I dont have that kind of money to have it repaired, this is what I have done so far. Cleaned the (MAF) by spraying break cleaner and waited for it to dry before reinstalling, checked PVC hoses and found that the elbow rubber pipes are cracked and one of them had a hole on it, I replaced the elbow pipes as well as the hoses, bought a new gas cap, reseted the codes by disconnecting the battery for 15 minutes. The check engine light still comes on after driveing a few miles, it runs good but sometimes it shakes when I reach 40 mph but stops when I reach 45-50 mph, when I start with a cold engine it shakes badly but does not die and I can smell gas at the back of the truck but only on the outside by the gas tank and the smell is pretty strong I look down the vehicle but does not see any drips. ANY SUGGESTIONS? To what might be causing this codes?