Hi Dave, it's amazing how a fuel tank setup can work perfectly in every situation except one. I Had the same experience today with my new Hangar9 Phoenix7. I rebuilt the tank floor from the factory setup to get perfect tank position and today while test flying the plane my buddy and I both commented about the very consistent needle setting from full to empty and every attitude, we flew every type maneuver to check the tank position and it worked perfect except for the last quarter of the slow roll. It will consistently hiccup but keep running. It does not hiccup on the eight point roll!. Conclusion, the clunk weight is to light and not keeping up with the fuel when the attitude changes slowly. you may have a similar problem. Oh BTW I love the Hangar9 Phoenix7, I flew the original in contest in the 70's. Good Luck