Hi everyone,
I know I have no responses to my thread but I have fixed the problem thanks to another forum post for a different year and different problems. So I am posting back to tell everyone what to check if their taillights start acting funny.
All you need to do is get under your truck in the back and find the ground for the lighting mine was on the driver side frame at the back on the inside. I just pulled it and cleaned the surface, bolt, and wire connection with a wire brush and all is well. Trust me try this first it will take about 5-10 minutes and if it isn't the problem all it means is that you have a better connecting ground. I spent probably 4 - 5 hours on other things and hours upon hours searching the web for an answer and now that you have read my post you might be able to skip all those hours and fix it in 5 - 10 minutes. All you need to do this on a 91 S10 truck is a ratchet with an extension and a 13 mm bit. Hope this helps someone in my same situation later on!
kadafi
P.S. The other post said there could be multiple grounds 1 for each light even. Find the wiring harness and follow it and find where a wire goes out and bolts down to the body on all 4 corners if necessary. My 91 only had 1 in back and it fixed it.