Yesterday I swapped converters on my truck at my buddy's house 50 miles from home. My gas mileage has always been horrible. I used a little more than 10 gallons of gas to get there. The old verter was at least a 12 inch diameter. Don't know what brand/stall it was. The new one is a 10" rated at 2200-2500 and really doesn't "feel" much different than my unknown verter but the fuel usage on the way back was awesome!. It only used about 3 gallons. Could it be the new smaller verter is just designed to be more efficient? OR was the old one worn out or defective?.

I'd guess the old one was worn out.

What are some symptoms that a converter is worn out or bad?. I was expecting to see more of a launching difference with the new converter.