Now that You all have made me dizzy,..... The GXP does Not share the same alternator as the 3800. The 3800 uses Napa #139190, the GXP uses#139187. From viewing other parts sources as well, I can safely say they are not the same , Or interchangable.
Vehicle:2005 PONTIAC BONNEVILLE V6-231ci 3.8L F/I Vin K
Product:Electrical - Alternator & Voltage Regulator
Select Part Number Manufacturer Catalog Description Your Price
ACDELCO US Generator $292.51
Alternator/Generator; 140 Amp (KG9) ; 140 ; Amps ; Except Bonneville Gxp (Wa2);Years: 2004-2005 ;Qty Per Vehicle:1
Anybody care to move it again.