Part of the problem with the GE T-64, according to many, was how it was installed in the boat. The engine was partially starved of air, due to the engine being installed "backwards". With the exhaust being routed forward, the upward exhaust was supposedly pushing the boat down while the rearward facing intake was trying to pull air out of a partial vacuum caused by the air flow around the cowling.
There could be some basis of fact in at least part of this as, two years later, the 8407, running as the Miss Budweiser T-1,with the engine replaced by the Lycombing T-55 installed with the intake forward, took the season high points championship. IIRC, the Bud team has issues running either T-1 or T-2 with a rear intake style "salt water" cowl as well. It was tried and, due to getting beat by at least the Miller, was not used again