904 Flares on 2-3 shift?

Pressure check like Sterling said. If the pressures look good check the front band adjustment. If it's real loose it can let it flare on shifts (all). If band adjustment is good time to come out and apart for inspection. They may have nicked a high clutch seal when rebuilding it. Most likely you'll find the high clutch burned since you've been driving it this way for a while. Could also be what Garrett said