i have a chevy express 3500, getting a random misfire on cylinders 1,5,8 changed plugs wires and coil packs. still doing the same thing.Transmission wont shift down to first gear,took it to dealer after trying another mechanic. Dealer says he thinks i have an electrical problem not a tranny problem maybe a short hes not sure and has no clue on misfires. Any help would be greatly appreciated. I havent had the van very long and it does have some miles on it but, surely its fixable?