A/C front not blowing at highway speeds

[mpicasso]

Have looked but have not seen anyone with same issue:

2006 Yukon XL Denali

When driving on highway for a period of time, front A/C vents stop blowing at the levels they should. Cycle to floor/defrost and nothing changes. Slow down to city driving and in less than 5 minutes, fan blows normal.

Do not recall having an issue with rear fans.

Not sure where/what to check as I cannot reproduce the results when at home.

Thanks in advance!!!

 

[mpicasso]

Update: seems to happen when driving highway speeds for a little while. Once I went back to lower speeds, no problems.
See attached photo - this is what I had after getting off the highway. Drove around another 30 mins, at lower speed, and never froze again.