The 4G is the workhorse of Mitsubishi. Reworked varients still available in the EVO. The engine itself is pretty robust, but Mitsubishi has always been known to screw up the slushboxes. I ws surprised to hear that you actually had such an old age on the vehicle given the tranny's repo, it should've been your second or third...lol.
As far as mileages go, there's alot of factors that affect the JDM or other spec engines when they run in Pakistan. Usually the cat converters are the first to go and the lead in the fuel plays havoc with the O2 sensors which over time really screw up your fueling. If experience is anything to go by, your exhaust is already short of a cat and your 02 went hibernating quite along ime ago.
The only thing you can check with the tranny is shift shock. It helps if you have an owners manual but as a rule of the thumb, the lock delay should'nt be more than 1.5 to 2 seconds when shifting into either reverse or drive from "P".
The original mileage specification for the Galant Es with the 4G63 was roughly 13k/l. factor in the wear and tear and so on. Should be about 9 off the top of my head.