2011 silverado showing limited to 89 klm per hour

Check injector pump pressure at injectors. Pump may be going out.

there is only estimated consumption because of the number of variables that effect it
tire pressure , drivers attitude, wind , load ,speed
10 ltr per 100 klm would be on the upper limit and 6 ltr per 100klm would be the lower limit if you have the vehicle you take it and fill it right up, set the trip meter to 00000
run it until is around 1/4 full then fill it right back up and take notice of the trip distance recorded
so if you have 400klm and you put in 40 ltr then that is 10 per 100

consumption is very much in the hands of the driver and his/her attitude
530 km on how many liter tank
Remember that the consumption is recorded as liters per 100 klm
However to ensure that the engine and transmission are performing to factory standards by having the fault codes read and fixing any faulty sensors found

check fuel pressure , fuel filter

Yes it will. Your having to depress the fuel pedal more and force more fuel into the engine. Eventually the engine will just stop running because the exhaust cannot get out.

That is near the border of the shift point. You may be able to influence it with accelerator or throttle positioner adjustment. That is only 49 mph.

1.3L 4cyl. Engine? Check Vacuum Lines to carb.

If the vehicle is in good condition, meaning all wheel bearings and tyre pressures are correct, at a cruising speed of one hundred and ten klm on the open road about eleven to twelve per litre....In town stop start driving....seven to eight per litre....Regards Johngee10

Cannot confirm. Need to verify other sensors are functioning properly--map sensor, tps, maf...is the engine light on?

If you have an autozone in your area, take it there. Ask them to plug in the obd unit and diagnose your issue. They can give you a printout of what the issue the obd is seeing, can sell you parts, and even show you how to replace whatever.

Semper Fi,
Z