Is it possible to create a better temperature controlling system?
I would recommend first contacting a home energy efficiency company first rather than an HVAC company. HVAC guys are usually clueless about systemic problems like these and will usually try to sell you a larger unit without diagnosing the true cause of the issue (which is a pain in the neck and can probably be fixed for much less than the cost of new equipment).

It sounds like you have two problems: Poor duct pressure and temperature stratification. These are likely caused by the same thing: conditioned air escaping or being wasted in some manner. A common cause is ductwork running through an unconditioned attic. For example, in a ranch house, if the A/C unit is on one side of the house, the register on the far side will often not be very cold because the heat of the attic is sucking out all the coolness in the ducts!

This is the kind of thing that is virtually impossible to diagnose over the internet. I would recommend contacting a local energy efficiency &amp; retrofit firm.