I was expirencing the same issue as you. First to second had a really bad delay and it was driving me crazy. Upon further investigation I found that my ground from the transmission to the chassis was really corroded. I decided to upgrade to 4 gauge wiring from the transmission to the chassis . I also made a ground cable from the engine to the transmission. The car shifts so much smoother now!! I would still check your transmission fluid and make sure its good. Let me know if you need pictures of the ground points.