i faced same sort of problem in my ride way back in 2001..at that time i had mehran...AC was doing a pretty good job but cabin wasnt loosing heat..then one fine day i put my bare foot on the floor of car...believe me it was burning....so i realised the cause of problem and insulated the floor and firewall with commonly available underlay used under carpets in homes using glue and put some extra foam near hinges of front doors. and it really helped in getting desired results.
when ac is on and outside temperature is very high then all the heat generated by engine, radiator and condensor is pushed towards firewall of body through exhaust thurt of fans, it heats up the firewall and undercarriage of body which reduces the cooling effect of AC. The silencer pipe also plays a big role in heating up the undercarriage.
do check the gear level assembly...there should not be any holes and damage to the rubber sealing the gear level assembly and cabin.
there are chances of entering hot air from the front doors. Make sure that they are properly sealed.
i beleive there is nothing wrong with roof isulation..as the air is best insulator and in khyber the space between roof lining and roof itslef is insulated by air.
wat i suggest is to take the seats out, remove the carpet and namda under it and put an uncut layer of jumbolon or underlay ( u can use dynamat as weel but they will csot u alot ) on floor. dont miss the firewall as it most imporatant.
then put back namba on floor and firewall and carpet on it.
im sure that after that you will feel noticeable difference in cooling and ac performace...
thanks