Paul,
That surge of energy may have been what I felt when I got the timing right when I was competing in T-38/T42 single hand distance back in the late 70s. It is quite a feeling and utilizing that increased line tension that it provides can be quite effective if done correctly. I believe that’s one of the factors that made me competitive back then (I was just a skinny lefthanded teenager casting right handed and build more like a long distance runner).
I don’t think that the “surge of energy… needs to dissipate.” The problem was likely instead how you started the FC. The surge will not case the rod tip to deflect if the angle between the line and the rod tip, or more correctly the direction of the force acting on the line—"the pull-angle”—is close to 180 degrees. Therefore, I don’t think one should start the FC with a rapid rotational acceleration, which will narrow the pull-angle—whether it be for tournament distance casting or normal fishing distances as that increases the risk of the rod tip dipping and raising and thus setting up small transverse waves at the start of the stroke (a narrow pull-angle combined with a too rapid start is also the reason why creeping and pushing increases the risk of tailing). It is better to instead start the FC by pulling the rod and line forward with the lower body and more gradually increase the degree of rotation. I don’t like the idea of “hitting it” as that suggest an abruptness in the stroke. You want a reasonably smooth and continuous acceleration and gradual change in the degree of rotation. It is not a constant acceleration or constant rotation, but smooth. The secrete is how you sequence the movement of the lower body, shoulders, arm, wrist and fingers, including so that they work together to create one fluid motion.
And yes, slide cannot occur after loop straight because of the loss of tension in the line. Starting with a rapid rotational acceleration when there is slack can also case the rod tip to deflect and rise and set up small transverse waves. I had assumed that is what happened and that you ended up starting the FC too late. There’s time lags between when we observing the loop straightening and when we are able start moving forward, and between the start of that movement and when it results in the leader start moving. One think that surprised me when I returned to competitive flycasting was how early many started the FC compared to what I was expecting. I just had a frame-by-frame look in Tracker at a video of Harald Økern Jensen (current trout distance WC) and myself casting ST27 on water and both of us started the next cast, including the final delivery, quite a bit before loop straight. There was also more line sag than expected (and tracking issues, which is what I wanted to look at). The video was filmed straight on from close to where the line landed. Quite interesting.
Nils
. I think this is a big contributor to why the distances are never that spectacular - or it could of course be because we're generally hung-over 
