1998 Hyundai Accent fixed loss of power w new plugs and wir

Transmission problem
1998 Hyundai Accent 4 cyl Front Wheel Drive Automatic 127k miles

Finally fixed my loss of power problem but my transmission does slip and had old fluid in it when I got the car, over 9 months I added a quart of fresh stuff and about 4.5 lucas oil stop slips and it works great.

Last night it lost power but in a different way when I paked it, a pool of tranny fluid under the air filter (which is above tranny) was bubbling and smoking, I know about the pool that built up and would soak it up whenever I had the chance knowing it needs a tranny flush or at least to drain out old fluid

My question, could it simply be the fact that I have waaay to much fluid in and it just bubbled out? Once it cooled off its been performing fine I added a little lucas oil stabilizer to it just to keep it lubbed and I would say is vented out almost a quart of excess fluid and im trying to open the drain plug to let the excess fluid out but its on there tight should I start by letting out excess fluid? Im afraid to do a full flush. Its been known to ruin the tranny all together ive been told, thanks -R