Improved mileage

I have a 2002 MAzda MPV that initially got 20mpg and gradually increased to 23mpg over 80,000. In May while away from home the transmission went kaput and would not stay in gear. I had it towed to a garage that I knew nothing about and was at their mercy. The owner determined that the hydrolic pump failed and would not hold the trans in gear. My options were a new Trans at $8000, a used as is trans at $2100 or him rebuilding mine for $2600. I chose the latter. It now shifts better than ever and on a recent 2000 mile trip to Colorado I averaged 26+mpg with the car top carrier on and driving 80mph in Nebraska and Colorado. What could the mechanic have done to get these improvements?

If the old transmission wasn’t producing enough hydraulic pressure, this can prevent the torque converter clutch from engaging. And if that happens, the vehicle gets less fuel mileage.

Tester

Would it have been this way from the day I bought it new?