Problem when car came back from shop

Hmmm.. You say you drove it some before the converter was installed and it seemed to work ok but now it doesn't. If your certain it did work right before I'd say it's a defective converter. If all he did was replace the filter and fluid and converter I don't know anything he could have "bumped" that would cause it to slip but did he adjust the bands by any chance? That would be the only thing I can think he might have done that would cause this problem?

BTW: No performance converter (hi stall) will act like that normally. I have a 3000 stall in my Cuda and it drives like a stock converter until I lay into it then it stalls to approx. 3000 rpm and gets with it.