2004 Pontiac Bonneville swapping transmissions

I want to swap transmissions from a parts vehicle to my 2004 Bonneville. My 04 has a slightly different gear ratio (FQ3, 2.86). The tranny I am about to install is the F83 with a 3.05 gear ratio. They both have codes MN3 and L36. Will this cause any problems? The parts man at a dealership thought it may mess up the computer and encouraged me to get the exact match. Is this necessary? Will it fit and work properly if I make this swap? Thanks. Notapromike