I agree with Cobalt-I'd drop the pan and be looking at the TCC lock-up solenoid. Before you drop the pan, go ahead and buy a new solenoid. They are cheap, and should be a part of any quality rebuild.
If you forgot to tighten the bolts that hold the L/U solenoid in place-that could be the problem as well. From my reading on how L/U works in these units, it is actually fluid pressure inside the converter that prevents the L/U clutches from engaging. Then, when the L/U solenoid is energized, it basically creates a leak path (bleed valve) that allows the pressure to bleed off and then the clutches apply. That L/U solenoid being faulty internally (stuck open) can cause this as well as if the solenoid is not bolted down firmly, or possibly the o-ring on the end is missing, or damaged. Get a new solenoid, drop the pan, and change it out. I'm hoping that will solve your issues.