Welcome to the Gulf Stream Owners RV Forum !!
I believe you should contact your dealer and tell him the results that the coach does not cool any better after installing "his" fix costing you the extra $$$. I would tell them they need to contact Gulf Stream to see how to proceed to correct this.
The dealer should have contacted Gulf Stream before installing the roof air and let them know there was a problem.
After all, common sense would tell them that if the basement airs can't cool the coach down to a set temperature for one of them to shut off, then the roof air will never run if the basement air has priority for the power (electricity).
Ron