The car is stalling within an allotted time of 20-30 minutes and as well as stalling at high speeds, such as 90.
Ever since, I had purchased this car, I quickly became aware of the butcher job the previous owners had done to the exhaust manifold, spark plug treads, head, wiring, thermostat etc.
After replacing the intake manifold, new manifold gasket, thermostat, head gasket, new spark plugs and fuel filter. It is still stalling, after three service technician at Canadian Tire told me:
"They just don't know." I'm running out of ideas to fix this car.
Sounds to me like your fuel pump/pressure is at fault here. Leave the car with your service dealer and make sure they diagnose the problem (properly) before you spend your money. I also suggest that you keep your gas level above 1/4 tank full to prevent crap from the bottom of the tank fouling your engine.
Try taking your car somewhere other than Canadian Tire. I know they have licensed technicians, but I have received nothing but brutal service with my vehicles there. They are handy because they are open longer hours than my regular mechanic, but I try to avoid them.