Climate Control , before I by Duovalve

I know this was talked about, but I just want to make sure once more before I change this part.

Heat works good through all settings, but sometimes goes crazy and starts blowing very hot air even at low TEMP setting, unless I press the COOL outside air button and then only center vents will do so.

When uing AC, Most of the times only the center vents blow cool, Defroster most always blows HOT and sides vents have a mind of their own, forcing me to only use center vents, meaning using a defroster in summer will sucks ass.

Sounds like an air distribution problem. Is it the DuoValve or the flaps not engaging properly.

Thanks.

Dave