In my opinion it sounds like you may have an exshaust value or two leaking around the valve guild,or you may have worn oil rings,if I had the car I would frist check the spark plugs to see which if any are getting fouled out then I'd check the compreshion in each cylinder to find out where the oil is coming from ether way you will be spending some money. Because ether you tear the engine down and fix it yourself or have a machanic do it, it's going to cost ya or you could call around to your local salvage yard to see if they would have a replacment engine for that one,now if I'm not mistaken your have a 4.9L engine depending on where you are in the U.S would depend on how much it's going to cost you. You can probably pick one up for around 400.00 to around 900.00 then get it installed. I wish good luck on it.