904 stuck in low gear

Sounds like the direct (front) clutches are toast. Repair and make certain the throttle linkage is adjusted properly or you will have problems.

Burnouts are critical with ALL Torqueflites. If you have an underpowered vehicle and are doing a burnout at the track with slicks, make sure the waterbox is good and wet or roll through and back-in again to paint-roller the tires good (rear only-lol). Start the tires turning ahead of the waterbox at mid-throttle in manual low and IMMEDIATELY shift to second and increase the throttle to maintain wheel speed (no bog). As quickly as possible, shift to "D" and maintain throttle or increase pedal until you are throwing some smoke. Then release your line-loc/brakes and as the vehicle rolls forward, release the gas and let the tires bite (chirp!!) while in HIGH gear. Roll to the lights and stage.

With a high-powered car or full race vehicle with slicks, do your water burnout starting in manual 2nd or high. NEVER let the tires bite except in HIGH gear, as this protects the transmission/low roller.