I wonder if my transmission or convertor is going. I replaced my engine last year. All else is the same. Car weight, 3.91's (and tires), T/A tight 10" convertor. My 65mph rpm with zero slip is 2944, from a calculator. The old engine did pretty close to that on the freeway, maybe 3K. With the new engine it's 3200rpm at 65. On same highway as well. Engines aren't huge difference, 499 vs 522. And besides its just driving on flat highway. I'm wondering if my trans/convertor is going south or is that increase the result of just more torque from the engine at that rpm causing a slight increase in stall? It seems ok otherwise but it's a high stall convertor so it's tough for me to judge it.
Same conditions as you stated (roadway, temps, etc.) and same axle ratio and tires you should have the same basic engine speed while cruising. That’s called road load.
It only takes x amount of power to move your car over a given road. You only use that much power to do so. Regardless how much the engine makes.
Engine torque and horsepower would affect slip while opening the throttle.
Hotter trans fluid will affect slip.
