What would cause your 1996 Cadillac to shudder and skip at 45 mph all the time?
Without knowing what "shudder and skip" means, but knowing that it occurs at a specific speed at all times, I might look to a gear noise issue. All gear sets have a noisy speed - They are generally engineered to occur at speeds that are not expected to be used as constant speeds of travel. In other words, they are designed to occur when you will only experience them for a short time, as you move through the 'noisy' speed. The shuddering and skipping might suggest that you have depleted or insufficient lubrication in the differential. Of course, this is an answer most applicable to a rear-wheel-drive system. ________________________________ If you have a front-wheel-drive vehicle: Is there a shift point near this speed? If so, then you may have a transmission 'dropping' into a gear that the vehicle is not 'ready' for? This could cause the engine to 'lug' and could generate a "shudder and skip" sensation. The problem would lie in the transmission.