A/c Fan Issue

[mrarivaca]

Just had the a/c fixed in my 01 Silverado 1500 HD 6.0 liter... new compressor, accumulator/dryer, orafice tube, high pressure switches. Here's the problem; turn it on and it works perfect, but after driving for about 25-30 mins, usually at hwy speeds, the fan kicks way down and hardly blows. I run thru all the fan speeds... you can hear the fan pick up but very little air comes out. It's as if something is partially blocking the air flow. I tried switching from re-circulate and back, but made no difference. If I exit the hwy and just let the truck idle for about 5 mins the fan starts blowing properly again. Any ideas what may be the cause? I'd appreciate any input. Thnx

 

Some one please help me out here... I've searched all the other post, but could not find a similar problem.