Originally Posted by bonnie94sse
That sounds interesting. Never heard of the "transmission lockup point". Could be the problem. I'll do what you said and see what happens. Thanks.
Well, I wouldn't call it a "problem" really; it'* what we in Tech Support call a "WAD" (Works as Designed).
47-48mph is the minimum point where the ECM allows the Torque Converter Clutch solenoid to lock the engine to the final drive and bypass the transmission'* torque convertor, which eliminates the normal slight slippage of the convertor and locks the engine directly to the drivetrain. (This is why, when the TCC solenoid gets stuck, the engine stalls when you come to a stop at the end of the expressway exit ramp or a stop sign, but restarts immediately when you put it in Park or Neutral.)
After lockup occurs, your RPMs will drop way down, so getting on the gas at that instant might feel kind of boggy as the ECM tries to decide whether to kick down out of lockup or just accelerate through it. Load factors determine what it should do -- gas pedal position, manifold vacuum (how much load the engine'* already got -- uphill, heavy load, etc.) -- and it'll either kick down for fast acceleration, or hold in lockup and look for boost from the supercharger.
I remember once on vacation after we crossed the Mississippi and started climbing uphill on the interstate at 80mph+ with a full load of people and luggage. I watched the supercharger boost gauge winding clockwise under cruise control and the car didn't miss a beat. We just sailed uphill past everybody else...