Sorry missed the to the floor part. I was having a similar issue. This would only happen when engine warm and semi hard acceleration. The car would accelerate very slowly but the tach would respond as if normal acceleration was happening.
It never triggered a code. Since I was changing the trans fluid I took a chance and changed the trans conductor plate. Solved 90% of my problem. I believe the speed sensor on the plate was acting up occasionally. The other 10% was the intercooler pump starting to go (only applies to SRT6).