Engine Exhaust System problems of the 1996 Nissan Nissan Truck

I have had an emissions problems (mil) continously since October 1996. The emission system was replaced by Nissan in 1998. The mil still comes on and I am getting about 16-17 mpg on 13. 59 gals. I have written letters to Nissan and have talked to numerous Nissan service personnel but have gotten nowhere. I tried going through better business bureau for arbitration but they told me I have too many miles on the pickup. The safety recall on the rear lights was never done, even though anderson Nissan in asheville, nc says it was done. They lied. I would appreciate all the help that you can give me, if any. The next step will have to be suing Nissan for breach of warranty. Breach of warranty because , even though they replaced the parts, they never fixed it. Thank you very much. Debbie.