@Maz, go for 5w-30 and reset the trip after that. take the car on any straight open road for 20-30 mins and you will get the best mileage your car is offering. also I agree with Ali on total, i had almost similar experience with all three brands except altron is generally very dirty (try putting in a clear bottle for 2-3 days).
also if you are very concerned about the mileage please do get the CAT washed, air filter cleaned/ changed, plugs replaced if necessary (Denso VKH20 or NKG ILFR6AIX-11 or any good long reach plug). you mentioned the new radiator can you send me a picture of the new one because a friend of mine is looking for a replacement but all he can find is 28 channel (naali) ones here in Rawalpindi.
@Ali: correct me if i am wrong but non-CVT takes 3L transmission oil and the CVT version takes 2.6 liters. in both cases they cant give you half can back, please make sure they filled it to the required level else you may face problems in future. generally with transmission oil change it is better to get the magnetic filter cleaned as well I know it needs opening the oil pan but it is a pretty safe procedure.