Truck is an 04 2500HD D-Max, plow is a MM2. This is the 5th year I've had this truck and plow and this just started last week. When I run the plow all lights dim; head lights, interior, backup, and the plow slows slightly. I had the batts checked and they're fine. I ran an additional ground from the batt the plow is wired to, no better. Any ideas? Bad alt?