Of course surface prep must be perfect with aluminum, even with GMAW.. Any surface oxides will promote lack of fusion..
Assuming good surface prep.
Spray transfer settings for your wire diameter could be between 400-470 ipm and between 22-28 Volts.
You want to use a push gun angle.
You should see spray from the end of your electrode wire but you need to keep the arc gap short (distance between the wire end and the base metal) 1/8" max..
If the electrode wire is stubbing into the work, increase voltage in 1/2 volt incraments until smooth spray.
If a long arc gap is observed, reduce voltage by 1/2 volt incraments until a nice shore arc gap is achieved. Long arcs tend to make the plasma cone bell shaped and undercut and fusion issues follow.
If you are using the GMAWP options than you would adjust the trim upward to increase the arc gap length and decrease the trim to reduce the arc gap length.
Many aluminum welders want to produce a whipped "row of dimes" appearence.. Only the most experienced welders can produce test quality welds with this technique.. Whipping spray transfer GMAW with aluminum can cause fusion issues both at the root and sidewall.
For performance testing (PQR or welder performance) use straight stringers to get best results... And since this is the method that produces best results, why not use it in production unless specs demand a ripple appearence.
Sometimes the XR feeders must also be calibrated to the power supply (accomplished between serial numbers and touchpad)... your owners manual or miller rep will be able to help with that.
Here are some factory parametershttp://www.hobartbrothers.com/pdf/datasheets/Smootharc5356.pdf
Also.. I'm in the upper Midwest too.. Wisconsin/Ill. stateline area.