What kind of mph? Thinking 123-125 range? Your combo seems pretty well setup as is. Might try more converter as you mentioned. Might be a simpler first step than getting into the tranny gears. But if you’re pulling it apart for a freshen up anyway then it’s just an argument with the wallet at that point.
For further reference, I footbrake off idle, flash to about 4,800 coming out of the hole, then drop to about 5,400 on the 6,800 shifts. I’m only 11.50s at 113-114 (send some air my way would ya?!?!)