Where you run the excess GPS antennae cord can make a difference!!
I just had my D3 installed in my '07 Hummer H2 and had very poor satellite reception. We took the dash apart and all connections were fine. The GPS antennae looked to be situated perfectly, just under the plastic dash, front, center at the windshield. The installed had "draped" the excess GPS antennae cord to the "right", over the HVAC duct, and it was free and clear of any obvious problems.
We went out for a spin with the dash off, and simply draped the excess cord to the "left" over the left HVAC duct and suddenly went from zero satellites to 4+. When we draped it back to the right, no satellites. Must have inadvertently had the excess cord near some type of magnetic interference.
Main point, if all connections are good with poor reception with the antennae in good location, try moving the pathway for the excess cord.
Hope this can help someone.