throttle body inj swap out??

If you are anywhere were emissions testing is required, this swap will be a tall tail. In SE Texas even if you manage to get the gasses out of the tail pipe to line up where it should, the engine lite will still be a problem. Here if it is on during an ASM test it is an automatic failure. May be stuck at the mileage that you are at with this one.

>> has a worn out throttle body<< What do you mean that it's 'worn out'? About the only thing to 'wear out' is the bushings on the throttle shaft that would cause a vacuum leak. A vacuum leak will be seen by the PCM as a lean condition, and will add fuel to compensate. And, the bushings can be replaced by anyone that does carb overhauling.
As far as fuel economy, a 4bbl won't give her any better. You are fighting the big tires and rear end gear ratio. Thermo-Quads were used on Chrysler products, Quadra-Jets on GMs. The computer in the vehicle is not adaptable for carburetion and will be opening a bucket of worms if you try to 'change it over'. Have you had the PCM scanned for trouble codes? Tire pressures? Tune parts? Injection service?

Sounds that some diagnostics need to be done before anything is done. The TBI may be fine. Could be the gasket between the TBI and intake manifold thats leaking...if it even has a vacuum leak. That hasn't been established, yet. The throttle body is a very simple device. It has an IAC (idle air control) motor attached to it that is controlled by the PCM (computer) which opens and closes at a very high rate of speed to contol air flow into the intake. On fuel injected vehicles, the fuel supply and pressure is constant. You add air to increase speed. Should be called an air pedal instead of a gas pedal. The two fuel injectors at the top of the TBI are supposed to supply a very fine spray of fuel. They are no more than electrical soleniods opening and closing depending on engine load. The amount of fuel required is controlled, again, by the PCM via engine sensors that give it the needed information. A properly working fuel injection system is by far superior to any carburetor in performance and fuel economy. The fuel injection system does require maintenance, just like any other mechanical item. It should be cleaned at 30-40K mile intervals.
If you have a vacuum leak, the MAP (manifold absolute pressure) sensor could be seeing a loss of vacuum, which it would see as the engine being under load and adding fuel. Of course, this would affect performance and fuel economy.
The CTS (coolant temp sensor) could be reading wrong and telling the PCM that you are in Fairbanks in January. It would tell the PCM to add fuel. The O2 (oxygen) sensor could also be faulty, giving the PCM incorrect info. Soooooooo,
have this diagnosed before you do anything. The diagnostic charge will more than likely save you money in the long run and will definitely control hair loss.

Hey, don't feel bad. You and I are only a year apart. It's really tough for us old pharts to try and keep up.
I'm not especially fond of TBI, either. Multi-port is sooooo much better! And, keeps improving. It's unbelievable to get 400hp out of a 350cu in engine and still get 20mpg. No chokes, no warm up in the mornings, ect....
But, there may be hope for me! I just bought an iPod. Downloaded all my 50's and 60's music to it. My wife said I'd ruin it by putting that stuff on it! Wrong.