2014 Enclave does not produce heat to the floor vents & defrost is marginal!!

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My 2014 Buick Enclave does not produce any heat to the floor vents for the driver & passenger. Brought it in for service at dealership - was told the in cabin air filter was plugged. This is only one year old. They tested the vent temperature to be 150 degrees - must have been the vents that blow to my hands and face, not my feet. I crank the temp to 90 degrees, fan on high and drive for 20-40 minutes and there is still NO heat coming out of the floor vent - defrost produces some warm air, but on long trips at 90 degrees blended, we are still cold in the front seats. Anyone else have a solution to this? Oh yeah, I was charged $60 to change that in-cabin air filter....