Whistling noise at speed of 55kmph and goes at speed of above 70 kmph

Most likely is the door seals, check there are no holes or splits. If it has always been the same it could be the mirrors. It depends lot on the age of the car as well, but I would check the door seals first.

Open the oil filler lid and see if the noise goes away - or lift the oil dip stick. It could be a gummed up PCV system that causes pressure in the crank case that "whistles" when the engine is running.

By opening the lid or dip stick, you're letting the pressure out and the whistling should stop.

If this is the issue, FCP Euro has a PCV replacement kit for about $350.

Check the windshield moldings for being loose.

First check your transmission fluid level before doing any test. Make certain this is not a speed vibration from the wheels by shifting the lever into 2 instead of D and reaching the speed you are having vibration at (as long as it is safe and you are not over reving the engine). While at that speed shift into D and let the transmission go into it's normal gear ranges and take note if the vibration occurs. I've seen (felt) this type of vibration many times on vehicles where the fluid is low. Adding fluid to the proper level solved this issue on some but on others there was existing transmission wear that this would not help. This doesn't mean the entire transmission is bad as the valve body inside the transmission fluid pan can sometimes cause this. Swapping out the valve body can be pricey but not as pricey as a new transmission and sometimes cheaper then having a used transmission installed.

Check to ensure that the overdrive is on or you will be running at high revs in top gear.
The airconditioning usually switches on another fan so that can help cooling.
Often a cooling system can cope with lower speed running but faster and longer trips show up faults in several possible areas:
thermostat sticking or only opening partially.
radiator partially blocked.
electric fan not operating.
The above three should be tested.
The timing may be out but it is set by computer and would have to have cambelt setting wrong to cause overheating.
Waterpumps can wear the impellor but again is rare.

sounds like a cv joint to me. That is what usually occurs when one is showing wear. C.V joints usually wear out between 80,000 and 120,000 k.m.

THAT sounds like a bearing in either /Alternator/belt
idler/water pump/or powered steering.
You say when it get to 70 but what is the rpm not speed as all pullys are differant sizes so rotate differant speeds OR check the power steering belt and others for cracks or loose.

First I need to ask is it a 4 speed or a 3 speed transmission. If it's a 4 speed when driving down the road pull it from drive to third gear. You shpuld hear the engine speed up if it does not then that means you have on 4th gear and you will have to take it to a transmission shop. If it's a 3 speed then just count the shift points if all 3 gears are present then drive down the road and see if the van goes into tcc. When you mean the rpms are high how high are they.

I don't know how loud the noise is, but its weird that you mention 50 mph. At that speed or above you are keep a constant rpm level. I say this because it might just be your air box loose and the sound of the intake air is making it. A 2008 truck should not have any major problem. Sometimes an alternator will sing or whine but never heard anyone say something is whistling. One other thing is sometimes for some reason ive heard a noise like that coming from the speakers of my car that goes up and down with the speed of the motor, but that was when I was tinkering with speakers and sub outs and amps. Thats all I can think of.

I had a problem with a whistling car after 50 mph and it turned out to be the front window gasket. I put silicone on the trim and problem solved.