Torque Converter? Where am I at? What is compromised?

With 3.91s, 28.2s , a TF automatic, and the GVod, the math is
(70 x1056 x3.91 x .78) divided by
( 28.2 x 3.1416)=2545rpm@ zero-slip
If your tach is accurate then (2700/2545) =1.061 so 6.1% slip; seems a lil excessive for a Scamp. More typical is 2/3%
What is your cruise timing? I bet not enough,lol. Ima thinking your combo will like 50 to 56 degrees. If, with your vacuum advance, you are only running say 40*, then 50/55 will greatly increase your cruise torque, and that should show up as a lower cruise rpm, which would translate to less slip.
3% up from the calculated 2545, is 2620. I use a digital tach for this kind of work, cuz the width of my tach needle is like a hundred rpm.