From what you're saying, when the engine has a load on it is the only time it bogs. Sounds like something is just coming to the end of its life (wearing out). What is the mileage on it? Has it ever had a tune up? If the carb has been cleaned before AND you smell like gas, could be a sign of the carb not being properly rebuilt. An oil leak wouldn't cause this type of concern, cause when there's no oil bad things happen and you're collecting pieces of your motor off the highway. Without being able to see, hear, and feel what's happening it's difficult to accurately narrow down what components could be the cause of your problem. It could very well be getting too much fuel instead of not enough. In which case your carb would be the first place to check. Or it could be that your engine is misfiring when under a load sending the unburnt air/fuel mixture out the exhaust. If it was my vehicle, I'd want to inspect the plugs for excessive plug gap first since they are easy to get out.
But what is the mileage on your vehicle? Most vehicle should have a basic tune up (spark plugs, plug wires, and induction service) every 100k miles, that's usually about how long spark plugs last with mild to medium driving habits.