I see in your signature that you have Bosch plugs and wires. How old are they? Those plugs and wires are junk in our 3800s. I would consider changing those before you pour money into the tranny. You have low miles for a tranny failure unless you've seriously been beating on it.
Pick up a set of NGK TR-55 plugs and a set of AC Delco plug wires.
Also, how old is your fuel filter? And have you checked your fuel pressures? Your pump may be getting weak.
I had a similar situation in my 99 that I couldn't resolve. Ended up being a weak fuel pump. Was only delivering 37 lbs. of fuel to the rail.
Let'* start with some cheap stuff first before you dump money into the tranny!