[Gunny]

On my '90 I've run both the 2.5 Borla and the larger Borla Challenger with & without headers and with & without cats. Some drone was always there regardless of the setup and, like you, bothered me only on trips. My solution was to drop to 5th unless I could get above 2K rpm in 6th. I experimented with a temporary solution by blocking off one tip on each muffler and this did eliminate the drone. I never did figure out how to install a flapper in one of the tips on each side as many have done with other setups. My ultimate solution was to install a stock LT4 system behind the SW headers and install QTP electric cutouts at the entrance side of each muffler. The result - no drone with cutouts closed or even partially open; with the cutouts totally open I'm running an open exhaust w/headers (the LT4 resonator is not restrictive at all) - the sound is awesome and there is plenty of drone, but open cutouts are not for interstate cruising anyway.

Good luck on finding a solution - Borlas are great sounding but there is always some drone at certain RPMs.