TH350 and the 1/4 mile

[Irishpilot]

Hey all, before the summer ended, I got my truck pieced back together and took it to the drag strip in Utah. I having a hell of a time with the tranny shifts, as the TH350 was shifting at 4,200 rpm, where I wanted it shifting at 6,000 as the engine I built can handle the revs. As is at 4,000' elev, it ran 15.0 @95mph, but I know she's got a lot more in her.

I adjusted the vacuum port screw on the tranny, but it only increased the shifts by 200 rpms. Besides holding the transmission in gears manually (which I really don't want to do), what can I do? I've heard that tranny shops can adjust the valves and weights internally to get the shifts. Has anyone done this, and if so how are the street manners? Thanks!