Air Conditioning - Poor AC Circulation... Sweltering... Help!!!

We purchased a 1996, 1,852 sq. ft., double wide mfg'd home approx. 1 month ago. As summer temps rise, our AC is less and less able to keep the house cool (some of the output vents blow cool air nicely... most do not). A technician came out 2 days ago and recharged the coolant and checked our system. He said that while our system is sufficient for the size of our house, the blower is not and should be replaced. The blower currently puts out 1023 CFM... we need 1400 to 1500 for a 3.5 ton system. Because he can't fit us in his busy schedule for several weeks, we called another company. They quoted a price of almost $1,400 for parts and labor. For a few hundred dollars more, we could replace the whole system.
We want to buy the blower and install it ourselves but don't know where to start... from where to purchase the part to installing it correctly. Are we going to bite off more than we can chew?
Our system is an INTERTHERM.

Please help... we're melting! ;)

Before jumping off the deep end, you need to know if indeed the blower is improperly sized or if there is duct leakage, or some type of restriction of the air flow. Manufactured homes are terrible when it comes to air flow. In 20 years in this business, I have never seen one to deliver uniform air flow without a major duct overhaul. These places are less expensive than site built housing for a reason. The blower might be the cause but it might not.

The tech told us, after climbing around under the house, that the duct work was fine and there appeared to be no leaks. He did agree with you about manufactured homes (here in lower DE, 70% of all homes are mfg'd) and the difficulties with AC/Heating. However, if we did install a more powerfull blower, would that help? Also, could we just replace just the blower motor? Again, this one is only a single speed 1023 CFM.
We have owned site built homes but this is our first mfg'd house. We purchased this as an investment (the property is worth far more than the house) and would prefer not to let this place nickel and dime us to death, ergo... we'd like to try do-it-yourself repairs when possible... we'd also love to be able to sleep in temperatures something less than 85 degrees.

What we both know about such repairs could be stuffed up a flea's nose and it would still bounce around like a beebee in a boxcar. Sigh....