when i drive around with my overdrive off my vents dont go wacky. Sup with that?

 

So as soon as you turn on your overdrive, it goes away?

 

I'm pretty sure that's a vacum issue. I see that you have 35" tires. Unless you have regeared your truck, it may have problems staying in overdrive. With the engine struggling to keep those big tires rolling in too high of a gear, you're getting sporatic vacum, which plays a big part in the A/C.

 

In o/d at about 75 the a/c stays on. any slower i have to turn the o/d off , and take my foot off the gas for a bit. The rpm is a little too high driving at highway speeds with the overdrive off. Can i rig my vent open somehow? I was also told that 2 new check valves will do the trick.