The torque converter cannot change the line pressure. The lugs on the converter are what drives the pump. There's no way to modify lugs. If the line pressure was low it'd affect the 1-2 shift also. How did you adjust the band (what method)?
If you had a stock or near stock stall converter in it before and you went to a pretty loose converter such as a 3000 stall or higher it will soften the shifts a little, but it won't cause the trans to flare up like your describing
