It's a 3500 stall and it is an 11" model so it's not the most efficient. According to my figures it's slipping 8%. Generally speaking even a good 3500 stall will slip 6% so mine's not that bad, just somewhat bad, LOL... I've seen some cheap converters slip 10% or more.
What gear are you running Del? What calculator did you use to figure it? Like I mentioned above a lot of calculators don't take into account any converter slip at all so their figures are off when using them to figure rpm with an automatic. That's why I like the calculator I posted the link to. It has a way to switch it to automatic trans and dial in some converter slippage