I regularly use fuel additives like dynotabs fuel tablet, available from adnoc gas station. They really work good in delivering clean fuel consumption and by adding extra octane to fuel. I feel good noticeable difference in car pickup and car fuel consumption.
Gear lever may be locked out, press the small key hole button next to gear lever by iserting some key and press it inside and at same time move the gear lever down to R. It will help.
If tires is too old, its ageing issue. If not its a manufacturing defect and no one cant do anything. If its new under warranty get it replaced free or else pay and get it change.
If its due to age, its better to change all 4 at one time so you will be trouble free for long time.
If not, due to some fault arose in rear shocks you are changing then dont change front ones.